2020-10-29T05:43:13Zhttp://edoc.mpg.de/ac_p_oai.ploai:edoc.mpg.de:53992006-10-1625:114
Cosmological smoothed particle hydrodynamics simulations: a hybrid multiphase model for star formation
Springel, Volker
Hernquist, Lars
methods : numerical; galaxies : evolution; galaxies : formation
We present a model for star formation and supernova feedback that describes the multiphase structure of star-forming gas on scales that are typically not resolved in cosmological simulations. Our approach includes radiative heating and cooling, the growth of cold clouds embedded in an ambient hot medium, star formation in these clouds, feedback from supernovae in the form of thermal heating and cloud evaporation, galactic winds and outflows, and metal enrichment. Implemented using smoothed particle hydrodynamics, our scheme is a significantly modified and extended version of the grid- based method of Yepes et al., and enables us to achieve a high dynamic range in simulations of structure formation. We discuss properties of the feedback model in detail and show that it predicts a self-regulated, quiescent mode of star formation, which, in particular, stabilizes the star-forming gaseous layers of disc galaxies. The parametrization of this mode can be reduced to a single free quantity that determines the overall time-scale for star formation. We fix this parameter numerically to match the observed rates of star formation in local disc galaxies. When normalized in this manner, cosmological simulations employing our model nevertheless overproduce the observed cosmic abundance of stellar material. We are thus motivated to extend our feedback model to include galactic winds associated with star formation. Using small- scale simulations of individual star-forming disc galaxies, we show that these winds produce either galactic fountains or outflows, depending on the depth of the gravitational potential. In low-mass haloes, winds can greatly suppress the overall efficiency of star formation. When incorporated into cosmological simulations, our combined model for star formation and winds predicts a cosmic star formation density that is consistent with observations, provided that the winds are sufficiently energetic. Moreover, outflows from galaxies in these simulations drive chemical enrichment of the intergalactic medium - in principle, accounting for the presence of metals in the Lyman alpha forest.
2003
Article
http://edoc.mpg.de/5399
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 289-311 (2003)
en
oai:edoc.mpg.de:54172006-10-1625:114
The resolved history of galaxy evolution
Brinchmann, J.
galaxy evolution; fundamental parameters of galaxies; stellar content of galaxies
We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology.
2002
Article
http://edoc.mpg.de/5417
urn:ISSN:1364-503X
Philosophical Transactions of the Royal Society of London Series A- Mathematical Physical and Engineeering Sciences, v.360, 2711-2723 (2002)
en
oai:edoc.mpg.de:54472006-10-1625:114
Halo concentrations and weak-lensing number counts in dark energy cosmologies
Bartelmann, M.
Perrotta, F.
Baccigalupi, C.
cosmology : theory; dense matter; gravitational lensing
We study the effects of a dark energy component with equation of state p = wrho with constant w greater than or equal to -1 on the formation of Cold Dark Matter (CDM) haloes. We find two main effects: first, haloes form earlier as w increases, and second, the amplitude of the dark-matter power spectrum gets reduced in order to remain compatible with the large scale Cosmic Microwave Background (CMB) anisotropies. These effects counteract. Using recipes derived from numerical simulations, we show that haloes are expected to be up to similar to50% more concentrated in CDM models with quintessence compared to LambdaCDM models, the maximum increase being reached for w similar to -0.6. For larger w, the amplitude of the power spectrum decreases rapidly and makes expected halo concentrations decrease. Halo detections through weak gravitational lensing are highly sensitive to halo concentrations. We show that weak-lensing halo counts with the aperture-mass technique increase by a factor of similar to2 as w is increased from -1 to - 0.6, offering a new method for constraining the nature of dark energy.
2002
Article
http://edoc.mpg.de/5447
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.396, 21-30 (2002)
en
oai:edoc.mpg.de:54572006-10-1625:114
Consistent beta values from density-density and velocity- velocity comparisons
Zaroubi, S.
Branchini, E.
Hoffman, Y.
da Costa, L. N.
galaxies : clusters : general; galaxies : distances and redshifts; cosmology : observations; cosmology : theory; large scale structure of Universe
We apply a new algorithm, called the unbiased minimal variance (hereafter UMV) estimator, to reconstruct the cosmic density and peculiar velocity fields in our local Universe from the SEcat catalogue of peculiar velocities comprising both early- (ENEAR) and late-type (SFI) galaxies. The reconstructed fields are compared with those predicted from the IRAS PSCz galaxy redshift survey to constrain the value of beta = Omega(m)(0.6) /b, where Omega(m) and b are the mass density and the bias parameters. The comparison of the density and velocity fields is carried out within the same methodological framework, and leads, for the first time, to consistent values of beta, yielding beta = 0.57(-0.13)(+011) and beta = 0.51 +/- 0.06, respectively. We find that the distribution of the density and velocity residuals, relative to their respective errors, is consistent with a Gaussian distribution with sigma approximate to 1, indicating that the density field predicted from the PSCz is an acceptable fit to that deduced from the peculiar velocities of the SEcat galaxies.
2002
Article
http://edoc.mpg.de/5457
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.336, 1234-1246 (2002)
en
oai:edoc.mpg.de:54712006-10-1625:114
1.65 micron (H band) surface photometry of galaxies. X. Structural and dynamical properties of elliptical galaxies
Zibetti, S.
Gavazzi, G
Scodeggio, M
Franzetti, P
Boselli, A
galaxies : elliptical and lenticular; cD; galaxies : fundamental parameters; galaxies : photometry; infrared : galaxies
We analyze the structural and dynamical properties of a sample of 324 nearby elliptical and dwarf elliptical galaxies observed during an extensive near-IR survey in the H band (1.65 mum). The fundamental plane is determined and a significant tilt is assessed. The origins of such a tilt are investigated by means of a spherically symmetric, isotropic, pressure-supported dynamical model relying on the observed surface brightness profiles. The systematic variation of the shape coefficient converting the measured central velocity dispersion sigma(0) into the virial rms velocity sigma(rms) is found to be the main cause of the tilt, due to aperture effects. Moreover, the ratio between the dynamical mass M-dyn and the total H-band luminosity L-H turns out to be roughly constant along the luminosity sequence of ellipticals: H-band luminosity is therefore a reliable and cheap estimator of the dynamical mass of the E galaxies.
2002
Article
http://edoc.mpg.de/5471
urn:ISSN:0004-637X
Astrophysical Journal, v.579, 261-269 (2002)
en
oai:edoc.mpg.de:54942006-10-1625:114
NGC 3628: Ejection activity associated with quasars
Arp, H.
Burbidge, E. M.
Chu, Y.
Flesch, E.
Patat, F.
Rupprecht, G.
galaxies : active; galaxies : individual : NGC 3628; quasars : general; radio lines : galaxies; X-rays : galaxies
NGC 3628 is a well-studied starburst/low level AGN galaxy in the Leo Triplet noted for its extensive outgassed plumes of neutral hydrogen. QSOs are shown to be concentrated around NGC 3628 and aligned with the HI plumes. The closest high redshift quasar has z = 2.15 and is at the tip of an X-ray filament emerging along the minor axis HI plume. Location at this point has an accidental probability of similar to2 x 10(-4). In addition a coincident chain of optical objects coming out along the minor axis ends on this quasar. More recent measures on a pair of strong X-ray sources situated at 3.2 and 5.4 arcmin on either side of NGC 3628 along its minor axis, reveal that they have nearly identical redshifts of z = 0.995 and 0.981. The closer quasar lies directly in the same X-ray filament which extends from the nucleus out 4.1 arcmin to end on the quasar of z = 2.15. The chain of objects SW along the minor axis of NGC 3628 has been imaged in four colours with the VLT. Images and spectra of individual objects within the filament are reported. It is suggested that material in various physical states and differing intrinsic redshifts is ejected out along the minor axis of this active, disturbed galaxy.
2002
Article
http://edoc.mpg.de/5494
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.391, 833-840 (2002)
en
oai:edoc.mpg.de:55312006-10-1625:114
Cluster detection from surface-brightness fluctuations in SDSS data
Bartelmann, M.
White, S. D. M.
methods : data analysis; techniques : image processing; surveys; galaxies : clusters : general; cosmology : observations
Galaxy clusters can be detected as surface brightness enhancements in smoothed optical surveys. This method does not require individual galaxies to be identifiable, and enables clusters to be detected out to surprisingly high redshifts, as recently demonstrated by the Las Campanas Distant Cluster Survey (LCDCS). Here, we investigate redshift limits for cluster detection in the Sloan Digital Sky Survey (SDSS). Calibrating assumptions about the surface brightness profile, the mass-to-light ratio, and the spectral energy distribution of galaxy clusters using available observational data, we show that it should be possible to detect galaxy groups out to redshifts of similar to0.5, and massive galaxy clusters out to redshifts of similar to1.2 in summed r' + i' + z' SDSS data. Redshift estimates can be derived from the SDSS magnitudes of brightest cluster members out to redshifts near unity. Over the area of sky it covers, SDSS should find greater than or similar to 98% of the clusters detectable by the Planck satellite through the thermal Sunyaev-Zel'dovich effect. The few Planck clusters not detected in SDSS will almost all be at z greater than or similar to 1.2.
2002
Article
http://edoc.mpg.de/5531
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.388, 732-740 (2002)
en
oai:edoc.mpg.de:55342006-10-1625:114
Correcting parameters of events based on the entropy of microlensing ensemble
Popowski, P.
Alcock, C.
dark matter; gravitation; gravitational lensing; methods : statistical; stars : fundamental parameters
We entertain the idea that robust theoretical expectations can become a tool in removing hidden observational or data- reduction biases. We illustrate this approach for a specific problem associated with gravitational microlensing. Using the fact that a group is more than just a collection of individuals, we derive formulae for correcting the distribution of the dimensionless impact parameters of events, u(min). We refer to the case when undetected biases in the u(min) distribution can be alleviated by multiplication of impact parameters of all events by a common constant factor. We show that in this case the general maximum likelihood problem of solving an infinite number of equations reduces to two constraints, and we find an analytic solution. Under the above assumptions, this solution represents a state in which the entropy of a microlensing ensemble is at its maximum; that is, the distribution of u(min) resembles a specific, theoretically expected, boxlike distribution to the highest possible extent. We also show that this technique does not allow one to correct the parameters of individual events on an event-by-event basis, independently from each other.
2002
Article
http://edoc.mpg.de/5534
urn:ISSN:0004-637X
The Astrophysical Journal, v.572, 514-520 (2002)
en
oai:edoc.mpg.de:55412006-10-1625:114
A conspicuous tangential alignment of galaxies in a STIS parallel Shear Survey field: A new dark-lens candidate?
Miralles, J. M.
Erben, T.
Hämmerle, H.
Schneider, P.
Fosbury, R. A. E.
Freudling, W.
Pirzkal, N.
Jain, B.
White, S. D. M.
gravitational lensing; cosmology : observations; dark matter
We report the serendipituous discovery of a conspicuous alignment of galaxies in a field obtained through the STIS Parallel Shear Survey. This project collects randomly distributed 50" x 50" fields to investigate the cosmic shear effect on this scale. Analyzing the parallel observations having the Seyfert galaxy NGC 625 as primary target, we recognized over the whole field of view a strong apparent tangential alignment of galaxy ellipticities towards the image center. The field shows several arclet-like features typical for images of massive galaxy clusters, but no obvious over- density of bright foreground galaxies. We also find a multiple image candidate. On the basis of the possible strong and weak lensing effect within the data, we discuss whether this could be compatible with a massive halo with no clear optical counterpart.
2002
Article
http://edoc.mpg.de/5541
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.388, 68-73 (2002)
en
oai:edoc.mpg.de:55542006-10-1625:114
Arguments for a Hubble constant near H-0=55
Arp, H.
Cepheids; galaxies : distances and redshifts
Recent analyses of Cepheid distances to spiral galaxies have led to the announcement of a Hubble constant of H-0 = 72 +/- 8 km s(-1) Mpc(-1). The new Cepheid distances, however, show that there are numerous redshift distances with large excesses that cannot be due to peculiar velocities. Ignoring these discordant redshifts, if the Hubble constant is calibrated with Cepheid distances of low-redshift spirals, then a value near H-0 = 55 is obtained. Use of independent distance criteria such as Tully-Fisher and group membership verifies this value and leads to three conclusions: ( 1) the peculiar velocities of galaxies in space are characteristically small; (2) Sc companions to normal Sb galaxies tend to be less luminous, with younger stellar populations and small amounts of nonvelocity redshift; and (3) ScI and other purportedly overluminous spiral galaxies have large amounts of intrinsic redshift.
2002
Article
http://edoc.mpg.de/5554
urn:ISSN:0004-637X
The Astrophysical Journal, v.571, 615-618 (2002)
en
oai:edoc.mpg.de:55552006-10-1625:114
Evolution and structure of magnetic fields in simulated galaxy clusters
Dolag, K.
Bartelmann, M.
Lesch, H.
magnetic fields; galaxies : clusters : general; cosmology : theory
We use cosmological magneto-hydrodynamic simulations to study the evolution of magnetic fields in galaxy clusters in two different cosmological models, a standard-CDM and a Lambda-CDM model. We show that the magnetic field strength profiles closely follow the cluster density profiles outside a core region of radius similar to200 h(-1) kpc. The magnetic field has a correlation length of order 50 h(-1) kpc and reverses on scales of similar to100 h(-1) kpc along typical lines-of-sight. The power spectrum of the magnetic field can well be approximated by a steep power law with an exponent of similar to-2.7. The mean magnetic field in the cluster cores grows roughly exponentially with decreasing redshift, Bsimilar to10(- 2.5z) muG. Merger events have a pronounced effect on magnetic field evolution, which is strongly reflected in measurable quantities like the Faraday rotation. The field evolution in the two different cosmologies proceeds virtually identically. All our cluster models very well reproduce observed Faraday rotation measurements when starting with nG seed fields.
2002
Article
http://edoc.mpg.de/5555
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.387, 383-395 (2002)
en
oai:edoc.mpg.de:55582006-10-1625:114
Redshifts of new galaxies
Arp, H.
Observations increasingly demonstrate the spatial association of high redshift objects with larger, low redshift galaxies. These companion objects show a continuous range of physical properties - from very compact, high redshift quasars, through smaller active galaxies and finally to only slightly smaller companion galaxies of slightly higher redshift. The shift in energy distribution from high to low makes it clear that are seeing an empirical evolution from newly created to older, more normal galaxies. In order to account for the evolution of intrinsic redshift we must conclude that matter is initially born with low mass particles whose mass increase with time (age). This requires a physics which is nonlocal (Machian) and which is therefore more applicable to the cosmos than the Big Bang extrapolation of local physics. Ambartsumian's "superfluid" foresaw some of the properties of the new, low particle mass, protogalactic plasma which is required, demonstrating again the age-old lesson that open minded observation is much more powerful than theoretical assumptions. Since the ejected plasma, which preferentially emerges along the minor axis of the parent galaxy, develops into an entire galaxy, accretion disks cannot supply sufficient material. New matter must be created within a "white hold" rather than bouncing old matter off a "black hole".
ASTRONOMICAL SOC PACIFIC
1999
Conference-Paper
http://edoc.mpg.de/5558
urn:ISSN:0074-1809
en
oai:edoc.mpg.de:55802006-10-1625:114
Cosmological information from quasar-galaxy correlations induced by weak lensing
Menard, B.
Bartelmann, M.
cosmology; large-scale structure of Universe; gravitational lensing
The magnification bias of large-scale structures, combined with galaxy biasing, leads to a cross-correlation of distant quasars with foreground galaxies on angular scales of the order of arcminutes and larger. The amplitude and angular shape of the cross-correlation function w(QG) contain information on cosmological parameters and the galaxy bias factor. While the existence of this cross-correlation has firmly been established, existing data did not allow an accurate measurement of wQG yet, but wide area surveys like the Sloan Digital Sky Survey now provide an ideal database for measuring it. However, wQG depends on several cosmological parameters and the galaxy bias factor. We study in detail the sensitivity of wQG to these parameters and develop a strategy for using the data. We show that the parameter space can be reduced to the bias factor (b) over bar, Omega(o) and sigma(8), and compute the accuracy with which these parameters can be deduced from SDSS data. Under reasonable assumptions, it should be possible to reach relative accuracies of the order of 5%-15% for (b) over bar, Omega(o), and sigma(8). This method is complementary to other weak-lensing analyses based on cosmic shear.
2002
Article
http://edoc.mpg.de/5580
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.386, 784-795 (2002)
en
oai:edoc.mpg.de:55902006-10-1625:114
The universal mass accretion history of cold dark matter haloes
van den Bosch, F. C.
stars : formation; galaxies : formation; galaxies : haloes; cosmology : theory; dark matter
We use the extended Press-Schechter formalism to investigate the rate at which cold dark matter haloes accrete mass. We discuss the shortcomings of previous methods that have been used to compute the mass accretion histories of dark matter haloes, and present an improved method based on the N-branch merger tree algorithm of Somerville & Kolatt. We show that this method no longer suffers from inconsistencies in halo formation times, and compare its predictions with high-resolution N-body simulations. Although the overall agreement is reasonable, there are slight inconsistencies which are most easily interpreted as a reflection of ellipsoidal collapse (as opposed to spherical collapse assumed in the Press-Schechter formalism). We show that the average mass accretion histories follow a simple, universal profile, and we present a simple recipe for computing the two scale-parameters which is applicable to a wide range of halo masses and cosmologies. Together with the universal profiles for the density and angular momentum distributions of cold dark matter haloes, these universal mass accretion histories provide a simple but accurate framework for modelling the structure and formation of dark matter haloes. In particular, they can be used as a backbone for modelling various aspects of galaxy formation where one is not interested in the detailed effects of merging. As an example we use the universal mass accretion history to compute the rate at which dark matter haloes accrete mass, which we compare with the cosmic star formation history of the Universe.
2002
Article
http://edoc.mpg.de/5590
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.331, 98-110 (2002)
en
oai:edoc.mpg.de:65722006-10-1625:114
Halo concentrations and weak-lensing number counts in dark energy cosmologies
Bartelmann, M.
Perrotta, F.
Baccigalupi, C.
Erratum - first version: Vol. 396 (2002) 21-30
2003
Article
http://edoc.mpg.de/6572
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.400, 19-19 (2003)
en
oai:edoc.mpg.de:97672006-10-1625:114
Measuring the virial masses of disk galaxies
van den Bosch, Frank C.
Springer
2003 Springer
2003
Conference-Paper
http://edoc.mpg.de/9767
urn:ISBN:3-540-00205-7
Bender, R.; Renzini, A.: The mass of galaxies at low and high redshift: Proceedings of the ESO/USM München Workshop, Springer, 250-255 (2003)
en
oai:edoc.mpg.de:97682006-10-1625:114
The origin of the correlation between the spin parameter and the Baryon fraction of galactic disks
Burkert, Andreas
van den Bosch, Frank C.
Swaters, Rob. A.
Springer
2003 Springer
2003
Conference-Paper
http://edoc.mpg.de/9768
urn:ISBN:3-540-00205-7
Bender, R.; Renzini, A.: The mass of galaxies at low and high redshift: Proceedings of the ESO/USM München Workshop, Springer, 119-123 (2003)
en
oai:edoc.mpg.de:97702006-10-1625:114
Flackerndes Licht vom Schwarzen Loch in KV UMa
Mathis, Hugues
Springel, Volker
Vandenhoeck & Ruprecht
2002 Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.
2002
InBook
http://edoc.mpg.de/9770
urn:ISBN:3-525-86132-X
Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.: Max-Planck-Gesellschaft - Jahrbuch 2002, 414-420 (2002)
de
oai:edoc.mpg.de:100452011-03-2125:114
Populating a cluster of galaxies - I. Results at z=0
Springel, V.
White, S. D. M.
Tormen, G.
Kauffmann, G.
galaxies : clusters : general; galaxies : formation; dark matter
We simulate the assembly of a massive rich cluster and the formation of its constituent galaxies in a flat. low-density universe. Our most accurate model follows the collapse, the star formation history and the orbital motion of all galaxies more luminous than the Fornax dwarf spheroidal, while dark halo structure is tracked consistently throughout the cluster for all galaxies more luminous than the SMC. Within its virial radius this model contains about 2 x 10(7) dark matter particles and almost 5000 distinct dynamically resolved galaxies. Simulations of this same cluster at a variety of resolutions allow us to check explicitly for numerical convergence both of the dark matter structures produced by our new parallel N-body and substructure identification codes. and of the galaxy populations produced by the phenomenological models we use to follow cooling, star formation. feedback and stellar aging. This baryonic modelling is tuned so that our simulations reproduce the observed properties of isolated spirals outside clusters. Without further parameter adjustment our simulations then produce a luminosity function. a mass-to- light ratio, luminosity, number and velocity dispersion profiles, and a morphology-radius relation which are similar to those observed in real clusters. In particular, since our simulations follow galaxy merging explicitly, we can demonstrate that it accounts quantitatively for the observed cluster population of bulges and elliptical galaxies.
2002
Article
http://edoc.mpg.de/10045
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.328, 726-750 (2002)
en
oai:edoc.mpg.de:101192006-10-1625:114
Spatial correlation functions and the pairwise peculiar velocity dispersion of galaxies in the Point Source Catalog Redshift Survey: Implications for the galaxy biasing in cold dark matter models
Jing, Y. P.
Börner, G.
Suto, Y.
cosmology : theory; dark matter; galaxies : clusters : general; galaxies : distances and redshifts; large-scale structure of universe
We report on the measurement of the two-point correlation function and the pairwise peculiar velocity of galaxies in the IRAS Point Source Catalog Redshift (PSCz) Survey. We compute these statistics first in redshift space and then obtain the projected functions that have simple relations to the real- space correlation functions on the basis of the method developed earlier in analyzing the Las Campanas Redshift Survey (LCRS) by Jing, Mo, & Borner. We find that the real space two- point correlation function can be fitted to a power law xi(r) = (r(o)/r)(gamma) with gamma = 1.69 and r(o) = 3.70 h(-1) Mpc. The pairwise peculiar velocity dispersion (PVD) sigma(12)(r(p)) is close to 400 km s(-1) at r(p) = 3 h(-1) Mpc and decreases to about 150 km s(-1) at r(p) approximate to 0.2 h(-1) Mpc. These values are significantly lower than those obtained from the LCRS. In order to understand the implications of those measurements on the galaxy biasing, we construct mock samples for a low-density spatially flat cold dark matter model (Omega(o) = 0.3, lambda(o) = 0.7, Gamma = 0.2, sigma(8) = 1), using a set of high-resolution N-body simulations in a box size of 100, 300, and 800 h(-1) Mpc. Applying a stronger cluster underweight biasing (proportional toM(-0.25)) than for the LCRS (proportional toM(-0.08)), we are able to reproduce these observational data, except for the strong decrease of the pairwise peculiar velocity at small separations. This is qualitatively ascribed to the different morphological mixture of galaxies in the two catalogs. Disk-dominated galaxy samples drawn from the theoretically constructed GIF catalog yield results rather similar to our mock samples with the simple cluster underweight biasing. We further apply the phenomenological biasing model in our N-body mock samples, which takes account of the density-morphology relation of galaxies in clusters. The model does not reduce the velocity dispersions of galaxies to the level measured in the PSCz data either. Thus, we conclude that the PVDs of the PSCz galaxies require a biasing model that substantially reduces the PVD on small scales relative to their spatial clustering.
2002
Article
http://edoc.mpg.de/10119
urn:ISSN:0004-637X
The Astrophysical Journal, v.564, 15-22 (2002)
en
oai:edoc.mpg.de:103742006-10-1625:114
The history of star formation in a Lambda cold dark matter universe
Springel, Volker
Hernquist, Lars
methods : numerical; galaxies : evolution; galaxies : starburst
Employing hydrodynamic simulations of structure formation in a Lambda cold dark matter cosmology, we study the history of cosmic star formation from the 'dark ages' at redshift z similar to 20 to the present. In addition to gravity and ordinary hydrodynamics, our model includes radiative heating and cooling of gas, star formation, supernova feedback and galactic winds. By making use of a comprehensive set of simulations on interlocking scales and epochs, we demonstrate numerical convergence of our results on all relevant halo mass scales, ranging from 10(8) to 10(15) h(-1) M-.. The predicted density of cosmic star formation, , is broadly consistent with measurements, given the observational uncertainty. From the present epoch, gradually rises by approximately a factor of 10 to a peak at z similar to 5-6, which is beyond the redshift range where it has been estimated observationally. In our model, fully 50 per cent of the stars are predicted to have formed by redshift z similar or equal to 2.14, and are thus older than 10.4 Gyr, while only 25 per cent form at redshifts lower than z similar or equal to 1. The mean age of all stars at the present is approximately 9 Gyr. Our model predicts a total stellar density at z = 0 of Omega(star) = 0.004, corresponding to approximately 10 per cent of all baryons being locked up in long-lived stars, in agreement with recent determinations of the luminosity density of the Universe. We determine the 'multiplicity function of cosmic star formation' as a function of redshift; i.e. the distribution of star formation with respect to halo mass. At redshifts around z similar or equal to 10, star formation occurs preferentially in haloes of mass >10(8) -10(10) h(-1) M-., while at lower redshifts, the dominant contribution to comes from progressively more massive haloes. Integrating over time, we find that approximately 50 per cent of all stars formed in haloes less massive than 10(11.5) h(-1) M-., with nearly equal contributions per logarithmic mass interval in the range 10(10) -10(13.5) h(-1) M-., making up similar to70 per cent of the total. We also briefly examine possible implications of our predicted star formation history for reionization of hydrogen in the Universe. According to our model, the stellar contribution to the ionizing background is expected to rise for redshifts z > 3, at least up to redshift z similar to 5, in accord with estimates from simultaneous measurements of the H and He opacities of the Lyman-alpha forest. This suggests that the ultraviolet background will be dominated by stars for z > 4, provided that there are not significantly more quasars at high z than are presently known. We measure the clumping factor of the gas from the simulations and estimate the growth of cosmic H ii regions, assuming a range of escape fractions for ionizing photons. We find that the star formation rate predicted by the simulations is sufficient to account for hydrogen reionization by z similar to 6, but only if a high escape fraction close to unity is assumed.
2003
Article
http://edoc.mpg.de/10374
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 312-334 (2003)
en
oai:edoc.mpg.de:103752006-10-1625:114
Understanding the results of galaxy-galaxy lensing using galaxy-mass correlation in numerical simulations
Yang, Xiao Hu
Mo, H. J.
Kauffmann, Guinevere
Chu, Yao Quan
gravitational lensing; methods : statistical; galaxies : haloes; dark matter; large-scale structure of Universe
McKay et al. have recently used measurements of weak galaxy- galaxy lensing in the Sloan Digital Sky Survey to estimate the cross-correlation between galaxies and the projected dark matter density field. They have derived a relation between aperture mass within a radius of 260 h (-1) kpc, M (260), and lens galaxy luminosity that does not depend on galaxy luminosity, type or environment. In this paper, we study the cross-correlation between galaxies and dark matter using galaxy catalogues constructed from a high-resolution N -body simulation of a LambdaCDM universe. We show that the simulation reproduces the observational results reasonably well, except that the predicted mass-to-light ratio is about a factor of 2 too high. In the simulation, M (260) is approximately equal to the halo virial mass for L * galaxies. M (260) overestimates the virial mass for fainter galaxies and underestimates it for brighter galaxies. We use the simulations to show that under certain circumstances the halo virial mass may be recovered by fitting a Navarro-Frenk-White (NFW) profile to the projected galaxy-mass correlation function. If we apply our method to the observations, we find that L * galaxies typically reside in haloes of similar to2 x 10(12) h (-1) M., consistent with halo masses estimated from the observed Tully-Fisher relation. In the simulations, the halo virial mass scales with galaxy luminosity as L (1.5) for central galaxies in haloes and for galaxies in low-density regions. For satellite galaxies, and for galaxies in high-density regions, there is no simple relation between galaxy luminosity and halo mass and care must be exercised when interpreting the lensing results.
2003
Article
http://edoc.mpg.de/10375
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 387-396 (2003)
en
oai:edoc.mpg.de:103772006-10-1625:114
The phase-space structure of cold dark matter haloes : insights into the Galactic halo
Helmi, A.
White, Simon D. M.
Springel, Volker
methods : numerical; Galaxy : formation; Galaxy : halo; Galaxy : kinematics and dynamics; galaxies : clusters : general; dark matter
We study the formation of the halo of the Milky Way in a Lambda-cold dark matter (LambdaCDM) cosmology by scaling down a high-resolution simulation of the formation of a cluster of galaxies. We determine how much phase-space substructure is left over from the objects that merge to build up the present galaxy. We study the debris streams originating from such objects and find that their evolution can be explained simply in terms of the conservation of phase-space density. Analysing the mass growth history of our halo we find that its inner regions have been in place for more than 10 Gyr, but that the growth of the halo as a whole is more gradual, in agreement with other high-resolution simulations of dark matter haloes. Recent accretion contributes to the inner 10 kpc of the halo only at the 10(-4) level. Finally, we determine the number of dark matter streams as a function of distance from the centre of the halo. In the equivalent of the 'solar vicinity', we find that the dark matter is smoothly distributed in space, and that the velocity ellipsoid is formed by hundreds of thousands of streams, most of which have velocity dispersions of the order of 1 km s(-1) or less.
2003
Article
http://edoc.mpg.de/10377
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 834-848 (2003)
en
oai:edoc.mpg.de:103782006-10-1625:114
Testing theoretical models for the higher order moments of dark halo distribution
Casas-Miranda, R.
Mo, H. J.
Börner, G.
galaxies : clusters : general; galaxies : formation; galaxies : haloes; cosmology : theory; dark matter
Using high-resolution N -body simulations, we test two theoretical models, based either on spherical or on ellipsoidal collapse model, for the higher order moments of the dark matter halo distribution in cold dark matter (CDM) models. We find that a theoretical model based on spherical collapse describes accurately the simulated counts-in-cells moments for haloes of several mass ranges. It appears that the model using ellipsoidal collapse instead of spherical collapse in defining dark haloes is unable to improve the models for the higher order moments of halo distribution, for haloes much smaller than M * (the mass scale on which the fluctuation of the density field has a rms about 1). Both models are particularly accurate for the descendants of haloes selected at high redshift, and so are quite useful in interpreting the high- order moments of galaxies. As an application we use the theoretical model to predict the higher order moments of the Lyman break galaxies observed at z approximate to 3 and their descendants at lower redshifts.
2003
Article
http://edoc.mpg.de/10378
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 872-880 (2003)
en
oai:edoc.mpg.de:103822006-10-1625:114
The growth and structure of dark matter haloes
Zhao, D. H.
Mo, H. J.
Jing, Y. P.
Börner, G.
galaxies : clusters : general; galaxies : formation; cosmology : theory; dark matter; large-scale structure of Universe
In this paper, we analyse in detail the mass-accretion histories and structural properties of dark haloes in high- resolution N-body simulations. We model the density distribution in individual haloes using the Navarro-Frenk-White (NFW) profile. For a given halo, there is a tight correlation between its inner-scale radius r(s) and the mass within it, M- s, for all its main progenitors. Using this correlation, one can predict quite well the structural properties of a dark halo at any time in its history from its mass-accretion history, implying that the structure properties and the mass-accretion history are closely correlated. The predicted growing rate of concentration c with time tends to increase with decreasing mass-accretion rate. The build-up of dark haloes in cold dark matter (CDM) models generally consists of an early phase of fast accretion (where the halo mass M-h increases with time much faster than the expansion rate of the Universe) and a late phase of slow accretion (where M-h increases with time approximately as the expansion rate). These two phases are separated at a time when c similar to 4 and the typical binding energy of the halo is approximately equal to that of a singular isothermal sphere with the same circular velocity. Haloes in the two accretion phases show systematically different properties, for example, the circular velocity v(h) increases rapidly with time in the fast accretion phase but remains almost constant in the slow accretion phase, the inner properties of a halo, such as r(s) and M-s increase rapidly with time in the fast accretion phase but change only slowly in the slow accretion phase, the inner circular velocity v(s) is approximately equal to v(h) in the fast accretion phase but is larger in the slow accretion phase. The potential well associated with a halo is built up mainly in the fast accretion phase, while a large amount of mass can be accreted in the slow accretion phase without changing the potential well significantly. We discuss our results in connection with the formation of dark haloes and galaxies in hierarchical models.
2003
Article
http://edoc.mpg.de/10382
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 12-24 (2003)
en
oai:edoc.mpg.de:103832006-10-1625:114
The central mass distribution in dwarf and low surface brightness galaxies
Swaters, R. A.
Madore, B. F.
van den Bosch, Frank C.
Balcells, M.
galaxies : dwarf; galaxies : halos; galaxies : kinematics and dynamics
We present high-resolution Halpha rotation curves for a sample of 15 dwarf and low surface brightness galaxies. From these we derive limits on the slopes of the central mass distributions, using both a direct inversion of the rotation curves and detailed mass models. Assuming that the density distributions of dark matter halos follow a power law at small radii, rho(r) proportional to r(-alpha), we find inner slopes in the range 0 less than or similar to alpha less than or similar to 1 for most galaxies. Thus, even with the relatively high spatial resolution of the H rotation curves presented here, the inner slopes are poorly constrained. In general halos with constant density cores (alpha = 0) provide somewhat better fits, but the majority of our galaxies (similar to75%) are also consistent with alpha = 1, as long as the R-band stellar mass-to-light ratios are smaller than about 2. Halos with alpha = 1.5, however, are ruled out in virtually every case. In order to investigate the robustness of these results we discuss and model several possible causes of systematic errors, including noncircular motions, galaxy inclination, slit width, seeing, and slit alignment errors. Taking the associated uncertainties into account, we conclude that even for the similar to25% of the cases where alpha = 1 seems inconsistent with the rotation curves, we cannot rule out cusp slopes this steep. Inclusion of literature samples similar to the one presented here leads to the same conclusion when the possibility of systematic errors is taken into account. In the ongoing debate on whether the rotation curves of dwarf and low surface brightness galaxies are consistent with predictions for a cold dark matter universe, we argue that our sample and the literature samples discussed in this paper provide insufficient evidence to rule out halos with alpha = 1. At the same time, we note that none of the galaxies in these samples require halos with steep cusps, as most are equally well or better explained by halos with constant density cores.
2003
Article
http://edoc.mpg.de/10383
urn:ISSN:0004-637X
The Astrophysical Journal, v.583, 732-751 (2003)
en
oai:edoc.mpg.de:103882006-10-1625:114
The three-point correlation function of cosmic shear - I. The natural components
Schneider, P.
Lombardi, M.
cosmology : theory; gravitational lensing; large-scale structure of the Universe; cosmic microwave background
The three-point correlation function of cosmic shear, the weak distortion of the images of distant galaxies by the gravitational field of the inhomogeneous matter distribution in the Universe, is studied here. Previous work on three-point statistics of cosmic shear has mainly concentrated on the convergence, or on aperture measures of the shear. However, as has become clear recently for the two-point statistics of cosmic shear, the basic quantity that should be used is the correlation function: first, it is much easier to measure from observational data, since it is immune against complicated geometries of data fields (which contain gaps and holes, e. g. due to masking); second, all other (linear) two-point statistics can be expressed as integrals over the correlation function. The situation is the same for the three-point statistics. However, in contrast to the two-point correlation function, the invariants (with respect to rotations) of the shear three-point correlation function have not been employed yet. Here we consider the transformation properties of the shear three-point correlation function under rotations. We show that there are four complex linear combinations of components of the three-point correlation function, which we shall call "natural components", since they are multiplied just by a phase factor for arbitrary rotations, but do not mix. In particular, their moduli are invariant under rotations and thus (non- linear) invariants of the three-point correlation function. In terms of these natural components, the invariance of the statistical properties of the shear field under parity transformations are easily obtained. Our results do not apply only to cosmic shear, but also to other quantities with the same mathematical properties that of a polar. For example, practically every relation derived here applies also to the polarization of the cosmic microwave background radiation.
2003
Article
http://edoc.mpg.de/10388
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.397, 809-818 (2003)
en
oai:edoc.mpg.de:103972006-10-1625:114
The inner structure of ΛCDM haloes - I. A numerical convergence study
Power, C.
Navarro, J. F.
Jenkins, A.
Frenk, C. S.
White, S. D. M.
Springel, V.
Stadel, J.
Quinn, T.
gravitation; cosmology : theory; dark matter
We present a comprehensive set of convergence tests which explore the role of various numerical parameters on the equilibrium structure of a simulated dark matter halo. We report on results obtained with two independent, state-of-the- art, multi-stepping, parallel N-body codes: pkdgrav and gadget. We find that convergent mass profiles can be obtained for suitable choices of the gravitational softening, time-step, force accuracy, initial redshift, and particle number. For softenings chosen so that particle discreteness effects are negligible, convergence in the circular velocity is obtained at radii where the following conditions are satisfied: (i) the time-step is much shorter than the local orbital time-scale; (ii) accelerations do not exceed a characteristic acceleration imprinted by the gravitational softening; and (iii) enough particles are enclosed so that the collisional relaxation time- scale is longer than the age of the Universe. Convergence also requires sufficiently high initial redshift and accurate force computations. Poor spatial, time, or force resolution leads generally to systems with artificially low central density, but may also result in the formation of artificially dense central cusps. We have explored several adaptive time-stepping choices and we have obtained the best results when individual time- steps are chosen according to the local acceleration and the gravitational softening (Deltat(i) proportional to (epsilon/a(i) )(1/2)), although further experimentation may yield better and more efficient criteria. The most stringent requirement for convergence is typically that imposed on the particle number by the collisional relaxation criterion. This implies that, in order to estimate accurate circular velocities at radii where the density contrast may reach similar to10(6), the region must enclose of the order of 3000 particles (or more than a few times 10(6) within the virial radius). Applying these criteria to a galaxy-sized LambdaCDM halo, we find that the spherically averaged density profile becomes progressively shallower from the virial radius inwards, reaching a logarithmic slope shallower than -1.2 at the innermost resolved point, similar to0.005 r (200), with little evidence for convergence to a power-law behaviour in the inner regions.
2003
Article
http://edoc.mpg.de/10397
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.338, 14-34 (2003)
en
oai:edoc.mpg.de:104032006-10-1625:114
Pairwise velocity dispersion of galaxies at high redshift: Theoretical predictions
Zhao, D. H.
Jing, Y. P.
Börner, G.
cosmology : theory; galaxies : high-redshift; galaxies : kinematics and dynamics
We investigate the feasibility of determining the pairwise velocity dispersion (PVD) for Lyman break galaxies (LBGs) and of using this quantity as a discriminator among theoretical models. We find that within a given cosmological model, different schemes of galaxy formation lead to significant changes of the PVD. We propose a simple phenomenological model for the formation of LBGs, determined by the formation interval parameter Delta(z) and the halo mass threshold M-h. With a reasonable choice for these two parameters, our model predicts an occupation number distribution of galaxies in halos that agrees very well with the predictions of semianalytical models. We also consider a range of galaxy formation models by adjusting the two model parameters. We find that model LBGs can have the same two-point correlation function (TPCF) over the range of observable separations, even though the cosmology and/or galaxy formation model are different. Moreover, with similar galaxy formation models, currently popular cosmologies can result in both the same TPCF and the same PVD. However, with the same cosmology, different galaxy formation models may show quite different PVDs, even though the TPCF is the same. Our test with mock samples shows furthermore that one can discriminate among such models already with currently available observational samples ( if the measurement error of the redshift is negligible), which have a typical error of 80 km s(-1). The error will be reduced by a factor of 2 if the samples are increased 4 times. We also show that an erroneous assumption about the geometry of the universe and different infall models only slightly change the results. Therefore, the PVD will become another promising statistic to test galaxy formation models with redshift samples of LBGs.
2002
Article
http://edoc.mpg.de/10403
urn:ISSN:0004-637X
The Astrophysical Journal, v.581, 876-885 (2002)
en
oai:edoc.mpg.de:104272011-05-2325:114
An analytical model for the non-linear redshift-space power spectrum
Kang, X.
Jing, Y. P.
Mo, H. J.
Borner, G.
2002
Article
http://edoc.mpg.de/10427
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.336, 892-900 (2002)
en
oai:edoc.mpg.de:104492006-10-1625:114
Images for an isothermal ellipsoidal gravitational lens from a single real algebraic equation
Asada, H.
Hamana, T.
Kasai, M.
gravitational lensing; galaxies : general; cosmology : theory
We present explicit expressions for the lens equation for a cored isothermal ellipsoidal gravitational lens as a single real sixth-order algebraic equation in two approaches; 2- dimensional Cartesian coordinates and 3-dimensional polar ones. We find a condition for physical solutions which correspond to at most five images. For a singular isothermal ellipsoid, the sixth-order equation is reduced to fourth-order one for which analytic solutions are well-known. Furthermore, we derive analytic criteria for determining the number of images for the singular lens, which give us simple expressions for the caustics and critical curves. The present formulation offers a useful way for studying galaxy lenses frequently modeled as isothermal ellipsoids.
2003
Article
http://edoc.mpg.de/10449
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.397, 825-829 (2003)
en
oai:edoc.mpg.de:104512006-10-1625:114
Algebraic properties of the real quintic equation for a binary gravitational lens
Asada, H.
Kasai, T.
Kasai, M.
It has been recently shown that the lens equation for a binary gravitational lens, which is apparently a coupled system, can be reduced to a real fifth-order (quintic) algebraic equation. Some algebraic properties of the real quintic equation are revealed. We find that the number of images on each side of the separation axis is independent of the mass ratio and separation unless the source crosses the caustics. Furthermore, the discriminant of the quintic equation enables us to study changes in the number of solutions, namely in the number of images. It is shown that this discriminant can be factorized into two parts: One represents the condition that the lens equation can be reduced to a single quintic equation, while the other corresponds to the caustics.
2002
Article
http://edoc.mpg.de/10451
urn:ISSN:0033-068X
Progress of Theoretical Physics, v.108, 1031-1037 (2002)
en
oai:edoc.mpg.de:104532006-10-1625:114
Voids in the simulated local Universe
Mathis, H.
White, S. D. M.
galaxies : formation; galaxies : statistics; large-scale structure of Universe
We use simulations of the formation and evolution of the galaxy population in the local Universe to address the issue of whether the standard theoretical model succeeds in producing empty regions as large and as dark as those observed nearby. We follow the formation of galaxies in a Lambda cold dark matter universe and work with mock catalogues that can resolve the morphology of Large Magellanic Cloud sized galaxies, and the luminosity of objects six times fainter. We look for a void signature in sets of virialized haloes selected by mass, and in mock galaxy samples selected according to observationally relevant quantities, such as luminosity, colour or morphology. We find several void regions with diameter 10 h(-1) Mpc in the simulation where gravity seems to have swept away even the smallest haloes we were able to track. We probe the environment density for the various populations and compute luminosity functions for galaxies residing in underdense, mean density and overdense regions. We also use nearest-neighbour statistics to check possible void populations, taking L-* spirals as reference neighbours. Down to our resolution limits, we find that all types of galaxies avoid the same regions, and that no class appears to populate the voids defined by the bright galaxies.
2002
Article
http://edoc.mpg.de/10453
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.337, 1193-1206 (2002)
en
oai:edoc.mpg.de:104702006-10-1625:114
High-redshift galaxies and the Ly alpha forest in a cold dark matter universe
Croft, R. A. C.
Hernquist, L.
Springel, V.
Westover, M.
White, M.
cosmology : observations; cosmology : theory; intergalactic medium; large-scale structure of universe; methods : N-body simulations; quasars : absorption lines
We use a cosmological hydrodynamic simulation of a cold dark matter universe to investigate theoretically the relationship between high-redshift galaxies and the Lyalpha forest at redshift z = 3. Galaxies in the simulation are surrounded by halos of hot gas, which nevertheless contain enough neutral hydrogen to cause a Lyalpha flux decrement, its strength increasing with galaxy mass. A comparison with recent observational data by Adelberger et al. on the Lyalpha forest around galaxies reveals that actual galaxies may have systematically less Lyalpha absorption within 1 Mpc of them than our simulated galaxies. In order to investigate this possibility, we add several simple prescriptions for galaxy feedback on the intergalactic medium (IGM) to the evolved simulation. These include the effect of photoionizing background radiation coming from galactic sources, galactic winds whose only effect is to deposit thermal energy into the IGM, and another, kinetic model for winds, which are assumed to evacuate cavities in the IGM around galaxies. We find that only the latter is able to produce a large effect, enough to match the tentative observational data, given the energy available from star formation in the simulated galaxies. Another intriguing possibility is that a selection effect is responsible, so that galaxies with low Lyalpha absorption are preferentially included in the sample. This is also viable but predicts galaxy properties (including clustering) that are very different from the other scenarios.
2002
Article
http://edoc.mpg.de/10470
urn:ISSN:0004-637X
The Astrophysical Journal, v.580, 634-652 (2002)
en
oai:edoc.mpg.de:104712011-05-2325:114
Intergalactic shock acceleration and the cosmic gamma-ray background
Miniati, F.
acceleration of particles; radiation mechanisms : non-thermal; shock waves; methods : numerical; large-scale structure of Universe; gamma-rays : theory
We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral pi mesons generated in p-p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to less than or similar to1 per cent. Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.
2002
Article
http://edoc.mpg.de/10471
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.337, 199-208 (2002)
en
oai:edoc.mpg.de:107082011-03-1625:114
B1422+231: The influence of mass substructure on strong lensing
Bradac, M.
Schneider, P.
Steinmetz, M.
Lombardi, M.
King, L. J.
Porcas, R.
2002
Article
http://edoc.mpg.de/10708
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.388, 373-382 (2002)
en
oai:edoc.mpg.de:107092006-10-1625:114
Lyman continuum escape from an inhomogeneous interstellar medium
Ciardi, B.
Bianchi, S.
Ferrara, A.
radiative transfer; HII regions
We have studied the effects of gas density inhomogeneities on the escape of ionizing Lyman continuum (Lyc) photons from Milky Way type galaxies via 3D numerical simulations using the Monte Carlo radiative transfer code CRASH. To this aim a comparison between a smooth Gaussian distribution (GDD) and an inhomogeneous, fractal one (FDD) has been made with realistic assumptions for the ionizing stellar sources based on available data in the solar neighbourhood. In both cases the escape fraction f(esc) increases with ionization rate (N)over dot(gamma) (although for the FDD with a flatter slope) and they become equal at (N)over dot(gamma) = 2 x 10(50) s(-1) where f(esc) = 0. 11. FDD allows escape fractions of the same order also at lower (N)over dot(gamma) when Lyc photon escape is sharply suppressed by GDD. Values of the escape fraction as high as 0.6 can be reached (GDD) for (N)over dot(gamma) approximate to 9 x 10(50) s(-1), corresponding to a star formation rate (SFR) of roughly 2 M-circle dot yr(-1); at this ionizing luminosity the FDD is less transparent (f(esc) approximate to 0.28). If high-redshift galaxies have gas column densities similar to local ones, and are characterized by such high SFRs and by a predominantly smooth (i.e. turbulence-free) interstellar medium, our results suggest that they should considerably contribute to - and possibly dominate - the cosmic UV background.
2002
Article
http://edoc.mpg.de/10709
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.331, 463-473 (2002)
en
oai:edoc.mpg.de:107102006-10-1625:114
The angular momentum of gas in protogalaxies. I. Implications for the formation of disk galaxies
van den Bosch, F. C.
Abel, T.
Croft, R. A. C.
Hernquist, L.
White, S. D. M.
dark matter; galaxies : formation; galaxies : halos; galaxies : structure; methods : n-body simulations
We use numerical simulations of structure formation in a cold dark matter cosmology to compare the angular momentum distributions of dark matter and nonradiative gas in a large sample of halos. We show that the two components have identical spin parameter distributions and that their angular momentum distributions within individual halos are very similar, all in excellent agreement with standard assumptions. Despite these similarities, however, we find that the angular momentum vectors of the gas and dark matter are poorly aligned, with a median misalignment angle of similar to30degrees, which might have important implications for spin correlation statistics used in weak lensing studies. We present distributions for the component of the angular momentum that is aligned with the total angular momentum of each halo and find that for between 5% and 50% of the mass, this component is negative. This disagrees with the generally adopted universal angular momentum distribution, for which the mass fraction with negative specific angular momentum is zero. We discuss the implications of our results for the formation of disk galaxies. Since galactic disks generally do not contain counterrotating stars or gas, disk formation cannot occur under detailed conservation of specific angular momentum. We suggest that the material with negative specific angular momentum combines with positive angular momentum material to build a bulge component, and we show that in such a scenario the remaining material can form a disk with a density distribution that is very close to exponential.
2002
Article
http://edoc.mpg.de/10710
urn:ISSN:0004-637X
The Astrophysical Journal, v.576, 21-35 (2002)
en
oai:edoc.mpg.de:107112006-10-1625:114
Wide field weak lensing observations of A1835 and A2204
Clowe, D.
Schneider, P.
gravitational lensing; galaxies : clusters : individual : A1835; galaxies : clusters : individual : A2204; dark matter
We present mass reconstructions from weak lensing for the galaxy clusters A1835 and A2204 over 34' x 34' fields using data from the ESO/MPG Wide Field Imager. Using a background galaxy population of 22 < R < 25.5 we detect the gravitational shear of A1835 at 8.8sigma significance, and obtain best-fit mass profiles of sigma(v) = 1233(-70)(+66) km s(-1) for a singular isothermal sphere model and r(200) = 1550 h(-1) kpc, c = 2.96 for a "universal" CDM profile. Using a color-selected background galaxy population of 22 < R < 25.8 we detect the gravitational shear of A2204 at 7.2sigma significance, and obtain best-fit mass profiles of sigma(v) = 1035(-71)(+65) km s(-1) for a SIS model and r(200) = 1310h(-1) km s(-1), c = 6.3 for a "universal" CDM profile. The gravitational shear at distances greater than 10' is significantly detected for both clusters. The best fit weak lensing cluster masses agree well with both X-ray and dynamical mass measurements, although the central concentration of A1835 is much lower in the weak lensing mass profile than that measured by recent Chandra results. We suggest that this lower concentration is most likely a combination of contamination of the "background" galaxy population with cluster dwarf galaxies and the effect of a prolate or tri-axial cluster core with the major axis lying near the plane of the sky. We also detect a number of additional structures at moderate significance, some of which appear to be sub-haloes associated with the clusters.
2002
Article
http://edoc.mpg.de/10711
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.395, 385-397 (2002)
en
oai:edoc.mpg.de:107142006-10-1625:114
The impact of cooling and feedback on disc galaxies
van den Bosch, F. C.
galaxies : formation; galaxies : fundamental parameters; galaxies : kinematics and dynamics; galaxies : structure; dark matter
In the standard picture of galaxy formation, mass and angular momentum are the two main parameters that determine the properties of disc galaxies. The details of how the gas inside dark matter haloes is transformed into a luminous disc, however, depend strongly on the physics of star formation, feedback and cooling, which are poorly understood. The efficiencies of these astrophysical processes are ultimately responsible for setting the galaxy mass fractions f(gal) defined as the ratio of galaxy mass (disc plus bulge) to total virial mass. Therefore, if we could somehow determine f(gal) (M-vir) from observations of the luminous component of disc galaxies, this would allow us to put stringent constraints on the efficiencies of cooling and feedback. This, however, requires estimating the total virial mass, which is a delicate problem. In this paper we use detailed, analytical models for the formation of disc galaxies to investigate the impact that cooling and feedback have on their structural properties. In particular, we investigate which observables extracted directly from the models are best suited as virial mass estimators, and to what extent they allow the recovery of the model input parameters regarding the feedback and cooling efficiencies. Contrary to naive expectations, the luminosities and circular velocities of disc galaxies are extremely poor indicators of total virial mass. Instead, we show that the product of disc scalelength and rotation velocity squared yields a much more robust virial mass estimate, which allows a fairly accurate recovery of the galaxy mass fractions as a function of the virial mass. We also show that feedback can cause a narrow correlation between f(gal) and the halo spin parameter, as found recently by van den Bosch, Burkert & Swaters from an analysis of dwarf galaxy rotation curves. Finally, we investigate the impact that cooling and feedback have on the colours, metallicities, star formation histories and Tully- Fisher relation of disc galaxies.
2002
Article
http://edoc.mpg.de/10714
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.332, 456-472 (2002)
en
oai:edoc.mpg.de:107162006-10-1625:114
Unbiased reconstruction of the large-scale structure
Zaroubi, S.
methods : statistical; cosmology : theory; large-scale structure of Universe
We present a new unbiased minimal variance (UMV) estimator for the purpose of reconstructing the large-scale structure of the Universe from noisy, sparse and incomplete data. Similar to the Wiener filter (WF), the UMV estimator is derived by requiring the linear minimal variance solution given the data and an assumed a priori model specifying the underlying field covariance matrix. However, unlike the WF, the minimization is carried out with the added constraint of an unbiased reconstructed mean field. The new estimator does not necessitate a noise model to estimate the underlying field; however, such a model is required for evaluating the errors at each point in space. The general application of the UMV estimator is to predict the values of the reconstructed field in unsampled regions of space (e.g. interpolation in the unobserved Zone of Avoidance), and to dynamically transform from one measured field to another (e.g. inversion of radial peculiar velocities to over-densities). Here, we provide two very simple applications of the method. The first is to recover a 1D signal from noisy, convolved data with gaps, for example CMB time-ordered data. The second application is a reconstruction of the density and 3D peculiar velocity fields from mock SEcat galaxy peculiar velocity catalogues.
2002
Article
http://edoc.mpg.de/10716
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.331, 901-908 (2002)
en
oai:edoc.mpg.de:107172006-10-1625:114
Gas cooling in simulations of the formation of the galaxy population
Yoshida, N.
Stoehr, F.
Springel, V.
White, S. D. M.
methods : N-body simulations; galaxies : clusters : general; galaxies : evolution
We compare two techniques for following the cooling of gas and its condensation into galaxies within high-resolution simulations of cosmologically representative regions. Both techniques treat the dark matter using N-body methods. One follows the gas using smoothed particle hydrodynamics (SPH) while the other uses simplified recipes from semi-analytic (SA) models. We compare the masses and locations predicted for dense knots of cold gas (the 'galaxies') when the two techniques are applied to evolution from the same initial conditions and when the additional complications of star formation and feedback are ignored. We find that above the effective resolution limit of the two techniques, they give very similar results both for global quantities such as the total amount of cooled gas and for the properties of individual 'galaxies'. The SA technique has systematic uncertainties arising from the simplified cooling model adopted, while details of the SPH implementation can produce substantial systematic variations in the galaxy masses it predicts. Nevertheless, for the best current SPH methods and the standard assumptions of the SA model, systematic differences between the two techniques are remarkably small. The SA technique gives adequate predictions for the condensation of gas into 'galaxies' at less than one per cent of the computational cost of obtaining similar results at comparable resolution using SPH.
2002
Article
http://edoc.mpg.de/10717
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.335, 762-772 (2002)
en
oai:edoc.mpg.de:107222006-10-1625:114
Simulating the Sunyaev-Zeldovich effect(s): Including radiative cooling and energy injection by galactic winds
White, M.
Hernquist, L.
Springel, V.
cosmic microwave background; cosmology : theory; galaxies : clusters : general; large-scale structure of universe; methods : numerical
We present results on the thermal and kinetic Sunyaev-Zeldovich (SZ) effects from a sequence of high-resolution hydrodynamic simulations of structure formation, including cooling, feedback, and metal injection. These simulations represent a self-consistent thermal model that incorporates ideas from the "preheating " scenario while preserving good agreement with the low-density intergalactic medium at z similar to 3 probed by the Lyalpha forest. Four simulations were performed, at two different resolutions with and without radiative effects and star formation. The long-wavelength modes in each simulation were the same, so we can compare the results on an object-by- object basis. We demonstrate that our simulations are converged to the subarcminute level. The effect of the additional physics is to suppress the mean Comptonization parameter by 20% and to suppress the angular power spectrum of fluctuations by just under a factor of 2 in this model, while leaving the source counts and properties relatively unchanged. We quantify how non-Gaussianity in the SZ maps increases the sample variance over the standard result for Gaussian fluctuations. We identify a large scatter in the Y-M relation that will be important in searches for clusters using the SZ effect(s).
2002
Article
http://edoc.mpg.de/10722
urn:ISSN:0004-637X
The Astrophysical Journal, v.579, 16-22 (2002)
en
oai:edoc.mpg.de:107232006-10-1625:114
Non-Gaussian cosmic microwave background temperature fluctuations from peculiar velocities of clusters
Yoshida, N.
Sheth, R. K.
Diaferio, A.
gravitation; methods : N-body simulations; galaxies : clusters : general; cosmic microwave background; large-scale structure of Universe
We use numerical simulations of a (480 Mpc h(-1))(3) volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev-Zeldovich (SZ) effects will be highly non-Gaussian, and very different from the peak-height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak- height distributions. At fixed optical depth, the distribution of peak heights resulting from the kinematic effect is Gaussian, with a width that is approximately proportional to the optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass and the distribution of halo speeds is Gaussian, with a dispersion that is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter.
2002
Article
http://edoc.mpg.de/10723
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.328, 669-677 (2002)
en
oai:edoc.mpg.de:107282006-10-1625:114
Cosmological constraint from the 2dF QSO spatial power spectrum
Yamamoto, K.
methods : analytical; quasars : general; cosmological parameters; large-scale structure of Universe
We obtain constraints on the cosmological density parameters, Omega(m) and Omega(b), by comparing the preliminary measurement of the quasi-stellar object (QSO) power spectrum from the Two- Degree Field (2dF) QSO Redshift (2QZ) survey with results from an analytic technique of power spectrum estimation, described herein. We demonstrate the validity of the analytic approach by comparing the results with the power spectrum of an N -body simulation. We find a better fit to the shape of the QSO power spectrum for low-density models with Omega(m) = 0.1-0.4. We show that a finite baryon fraction Omega(b) /Omega(m) = 0.2, consistent with observations of the cosmic microwave background anisotropies and nucleosynthesis, fits the observational result of the 2QZ survey better, though the constraint is not very tight. By using the Fisher matrix technique, we investigate just how large a survey would be required before a significant constraint on the density parameters could be obtained. We demonstrate that the constraint could be significantly improved if the survey was four times larger.
2002
Article
http://edoc.mpg.de/10728
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.334, 958-962 (2002)
en
oai:edoc.mpg.de:107382006-10-1625:114
The mass function of dark matter haloes
Jenkins, A.
Frenk, C. S.
White, S. D. M.
Colberg, J. M.
Cole, S.
Evrard, A. E.
Couchman, H. M. P.
Yoshida, N.
gravitation; methods : numerical; cosmology : theory; dark matter
We combine data from a number of N-body simulations to predict the abundance of dark haloes in cold dark matter (CDM) universes over more than four orders of magnitude in mass. A comparison of different simulations suggests that the dominant uncertainty in our results is systematic and is smaller than 10-30 per cent at all masses, depending on the halo definition used. In particular, our 'Hubble volume' simulations of tau CDM and Lambda CDM cosmologies allow the abundance of massive clusters to be predicted with uncertainties well below those expected in all currently planned observational surveys. We show that for a range of CDM cosmologies and for a suitable halo definition, the simulated mass function is almost independent of epoch, of cosmological parameters and of the initial power spectrum when expressed in appropriate variables. This universality is of exactly the kind predicted by the familiar Press-Schechter model, although this model predicts a mass function shape that differs from our numerical results, overestimating the abundance of 'typical' haloes and underestimating that of massive systems.
2001
Article
http://edoc.mpg.de/10738
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.321, 372-384 (2001)
en
oai:edoc.mpg.de:107402006-10-1625:114
The trispectrum of the 4 year COBE DMR data
Kunz, M.
Banday, A. J.
Castro, P. G.
Ferreira, P. G.
Gorski, K. M.
cosmic microwave background; cosmology : observations
We propose an estimator for the trispectrum of a scalar random field on a sphere, discuss its geometrical and statistical properties, and outline its implementation. By estimating the trispectrum of the 4 yr COBE Differential Microwave Radiometer experiment data (in HEALPix pixelization), we find new evidence of a non-Gaussian signal associated with a known systematic effect. We find that by removing data from the sky maps for those periods of time perturbed by this effect, the amplitudes of the trispectrum coefficients become completely consistent with predictions for a Gaussian sky. These results reinforce the importance of statistical methods based in harmonic space for quantifying non-Gaussianity.
2002
Article
http://edoc.mpg.de/10740
urn:ISSN:0004-637X
The Astrophysical Journal, v.563, L99-L102 (2002)
en
oai:edoc.mpg.de:107422006-10-1625:114
Surface brightness fluctuations of Fornax Cluster galaxies: Calibration of infrared surface brightness fluctuations and evidence for recent star formation
Liu, M. C.
Graham, J. R.
Charlot, S.
distance scale; galaxies : distances and redshifts; galaxies : elliptical and lenticular; cD; galaxies : stellar content; infrared : galaxies
We have measured K-s-band (2.0-2.3 mum) surface brightness fluctuations (SBFs) of 19 early-type galaxies in the Fornax Cluster. Fornax is ideally suited both for calibrating SBFs as distance indicators and for using SBFs to probe the unresolved stellar content of early-type galaxies. Combining our results with published data for other nearby clusters, we calibrate K- s-band SBFs using Hubble Space Telescope (HST) Cepheid cluster distances and I-band SBF distances to individual galaxies. With the latter, the resulting calibration is (M) over bar (Ks) = (- 5.84 +/- 0.04) + (3.6 +/- 0.8)[(V - I-c)(o) - 1.15], valid for 1.05 < (V - I-c)(o) < 1.25 and not including any systematic errors in the HST Cepheid distance scale. The fit accounts for the covariance between V-I-c and (M) over bar (Ks) when calibrated in this fashion. The intrinsic cosmic scatter of (M) over bar (Ks) appears to be larger than that of I-band SBFs. S0 galaxies may follow a different relation, although the data are inconclusive. The discovery of correlation between K-s-band fluctuation magnitudes and colors with V-I-c is a new clue into the star formation histories of early-type galaxies. This relation naturally accounts for galaxies previously claimed to have anomalously bright K-band SBFs, namely, M32 and NGC 4489. Models indicate that the stellar populations dominating the SBF signal have a significant range in age; some scatter in metallicity may also be present. The youngest ages imply some galaxies have very luminous giant branches, akin to those in intermediate-age (few Gyr) Magellanic Cloud clusters. The inferred metallicities are roughly solar, although this depends on the choice of theoretical models. A few Fornax galaxies have unusually bright K-s-band SBFs, perhaps originating from a high-metallicity burst of star formation in the last few Gyr. The increased spread and brightening of the K-s-band SBFs with bluer V-I-c suggest that the lower mass cluster galaxies (less than or similar to 0.1 L*) may have had more extended and more heterogeneous star formation histories than those of the more massive galaxies.
2002
Article
http://edoc.mpg.de/10742
urn:ISSN:0004-637X
The Astrophysical Journal, v.564, 216-233 (2002)
en
oai:edoc.mpg.de:107482006-10-1625:114
Tests of the Las Campanas Distant Cluster Survey from confirmation observations for the ESO Distant Cluster Survey
Gonzalez, A. H.
Zaritsky, D.
Simard, L.
Clowe, D.
White, S. D. M.
galaxies : clusters : general; galaxies : elliptical and lenticular; cD; galaxies : high-redshift
The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic study of the galaxy cluster population at two epochs, zsimilar or equal to0.5 and zsimilar or equal to0.8, drawn from the Las Campanas Distant Cluster Survey (LCDCS). We report results from the initial candidate-confirmation stage of the program and use these results to probe the properties of the LCDCS. Of the 30 candidates targeted, we find statistically significant overdensities of red galaxies near 28. Of the 10 additional candidates serendipitously observed within the fields of the targeted 30, we detect red galaxy overdensities near six. We test the robustness of the published LCDCS estimated redshifts to misidentification of the brightest cluster galaxy ( BCG) in the survey data and measure the spatial alignment of the published cluster coordinates, the peak red galaxy overdensity, and the BCG. We conclude that for LCDCS clusters out to zsimilar to0.8, (1) the LCDCS coordinates agree with the centroid of the red galaxy overdensity to within 25"(similar to150 h(-1) kpc) for 34 out of 37 candidates with 3sigma galaxy overdensities, (2) BCGs are typically coincident with the centroid of the red galaxy population to within a projected separation of 200 h(-1) kpc (32 out of 34 confirmed candidates), ( 3) the red galaxy population is strongly concentrated, and ( 4) the misidentification of the BCG in the LCDCS causes a redshift error greater than 0.1 in 15%-20% of the LCDCS candidates. These findings together help explain the success of the surface brightness fluctuations detection method.
2002
Article
http://edoc.mpg.de/10748
urn:ISSN:0004-637X
The Astrophysical Journal, v.579, 577-586 (2002)
en
oai:edoc.mpg.de:107502006-10-1625:114
The N-point correlation functions of the COBE-DMR maps revisited
Eriksen, H. K.
Banday, A. J.
Gorski, K. M.
cosmic microwave background; cosmology : observations; methods : statistical
We calculate the two-, three- and (for the first time) four- point correlation functions of the COBE-DMR 4-year sky maps, and search for evidence of non-Gaussianity by comparing the data to Monte Carlo-simulations of the functions. The analysis is performed for the 53 and 90 GHz channels, and five linear combinations thereof. For each map, we simulate an ensemble of 10 000 Gaussian realizations based on an a priori best-fit scale-invariant cosmological power spectrum, the DMR beam pattern and instrument-specific noise properties. Each observed COBE-DMR map is compared to the ensemble using a simple chi(2) statistic, itself calibrated by simulations. In addition, under the assumption of Gaussian fluctuations, we find explicit expressions for the expected values of the four-point functions in terms of combinations of products of the two- point functions, then compare the observed four-point statistics to those predicted by the observed two- point function, using a redefined chi(2) statistic. Both tests accept the hypothesis that the DMR maps are consistent with Gaussian initial perturbations.
2002
Article
http://edoc.mpg.de/10750
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.395, 409-415 (2002)
en
oai:edoc.mpg.de:107792006-10-1625:114
Towards a model of full-sky Galactic synchrotron intensity and linear polarisation: A re-analysis of the Parkes data
Giardino, G.
Banday, A. J.
Gorski, K. M.
Bennett, K.
Jonas, J. L.
Tauber, J.
radio continuum : ISM; surveys; polarization; cosmic microwave background
We have analysed the angular power spectra of the Parkes radio continuum and polarisation survey of the Southern galactic plane at 2.4 GHz. We have found that in the multipole range l = 40-250 the angular power spectrum of the polarised intensity is well described by a power-law spectrum with fitted spectral index alpha(L) = 2.37 +/- 0.21. In the same multipole range the angular power spectra of the E and B components of the polarised signal are significantly flatter, with fitted spectral indices respectively of alpha(E) = 1.57 +/- 0.12 and alpha(B) = 1.45 +/- 0.12. Temperature fluctuations in the E and B components are mostly determined by variations in polarisation angle. We have combined these results with other data from available radio surveys in order to produce a full- sky toy model of Galactic synchrotron intensity and linear polarisation at high frequencies (nu greater than or similar to 10 GHz). This can be used to study the feasibility of measuring the Cosmic Microwave Background polarisation with forthcoming experiments and satellite missions.
2002
Article
http://edoc.mpg.de/10779
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.387, 82-97 (2002)
en
oai:edoc.mpg.de:107882006-10-1625:114
Constraints on reionization from the thermal history of the intergalactic medium
Theuns, T.
Schaye, J.
Zaroubi, S.
Kim, T. S.
Tzanavaris, P.
Carswell, B.
cosmology : observations; cosmology : theory; galaxies : formation; intergalactic medium; quasars : absorption lines
The temperature of the diffuse, photoheated intergalactic medium (IGM) depends on its reionization history because the thermal timescales are long. The widths of the hydrogen Lyalpha absorption lines seen in the spectra of distant quasars that arise in the IGM can be used to determine its temperature. We use a wavelet analysis of the Lyalpha forest region of quasar spectra to demonstrate that there is a relatively sudden increase in the line widths between redshifts z approximate to 3.5 and 3.0, which we associate with entropy injection resulting from the reionization of He II. The subsequent falloff in temperature after z approximate to 3.5 consistent with a thermal evolution dominated by adiabatic expansion. If, as expected, the temperature also drops rapidly after hydrogen reionization, then the high temperatures inferred from the line widths before He II reionization imply that hydrogen reionization occurred below redshift z = 9.
2002
Article
http://edoc.mpg.de/10788
urn:ISSN:0004-637X
The Astrophysical Journal, v.567, L103-L106 (2002)
en
oai:edoc.mpg.de:107912006-10-1625:114
Temperature fluctuations in the intergalactic medium
Theuns, T.
Zaroubi, S.
Kim, T. S.
Tzanavaris, P.
Carswell, R. F.
hydrodynamics; intergalactic medium; quasars : absorption lines; cosmology : theory; large-scale structure of Universe
The temperature of the low-density intergalactic medium (IGM) is set by the balance between adiabatic cooling resulting from the expansion of the Universe, and photoheating by the ultraviolet (UV) background. We have analysed the Lyalpha forest of 11 high-resolution quasar spectra using wavelets, and find strong evidence of a marked jump in the temperature at the mean density, T (0) , of 60+/-14 per cent over the redshift interval z =[3.5,3.1], which we attribute to reionization of He ii. The jump can be seen in all three of our spectra that straddle redshift 3.3, at a significance of greater than or equal to99 per cent. Below z similar to3.1, our results are consistent with a smooth cooling down of the universe, as expected when adiabatic expansion dominates over photoheating by a UV background from quasi-stellar objects (QSOs) and galaxies. We find no evidence of thermal fluctuations on scales greater than or equal to5000 km s(-1) larger than 50 per cent, which could be detected by our method, suggesting that the IGM follows a reasonably well-defined temperature-density relation. We demonstrate that the mean wavelet amplitude <A >proportional to1/T (0), and calibrate the relation with hydrodynamical simulations. We find T-0 greater than or equal to1.2x10(4) K at z greater than or equal to3.6. Such high temperatures suggest that H i reionization occurred relatively recently.
2002
Article
http://edoc.mpg.de/10791
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.332, 367-382 (2002)
en
oai:edoc.mpg.de:107932006-10-1625:114
Multiple supermassive black holes in galactic bulges
Haehnelt, M. G.
Kauffmann, G.
black hole physics; binaries : general; galaxies : formation; galaxies : nuclei
We study the number and interaction rates of supermassive black holes in galactic bulges as predicted by hierarchical models of galaxy formation in which the spheroidal components of galaxies are formed by mergers. In bright ellipticals, the number of events that can eject a central supermassive binary black hole is large. Central binaries must therefore merge in less than a Hubble time - otherwise there will be too much scatter in the M - relation and too many off-centre galactic nuclei. We propose that binary black holes are able to merge during the major gas accretion events that trigger QSO activity in galaxies. If this is the case, less than 10 per cent of faint ellipticals and 40 per cent of bright ellipticals are predicted to harbour binary black holes with near equal masses at their centres. This binary may be ejected away from the centre of the galaxy or even into intergalactic space in up to 20 per cent of the most luminous ellipticals. The number of low-mass black holes that can interact with the central object is predicted to be a strong function of galaxy luminosity. In most faint ellipticals, no black holes fall into the centre of the galaxy after the last major gas accretion event, but in the most luminous ellipticals, an average of 10 low-mass black holes interact with the central supermassive object after this time. It is expected that stars will be ejected from galaxy cores as these low mass ratio binaries harden. Multiple black holes in galactic bulges thus provide a natural explanation for the strong systematic trends in the observed central density profiles of ellipticals as a function of luminosity.
2002
Article
http://edoc.mpg.de/10793
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.336, L61-L64 (2002)
en
oai:edoc.mpg.de:107952006-10-1625:114
The satellite population of the Milky Way in a Lambda CDM universe
Stöhr, F.
White, S. D. M.
Tormen, G.
Springel, V.
methods : N-body simulations; galaxies : evolution; galaxies : formation; Local Group; dark matter
We compare the structure and kinematics of the 11 known satellites of the Milky Way with high-resolution simulations of the formation of its dark halo in a LambdaCDM universe. In contrast to earlier work, we find excellent agreement. The observed kinematics are exactly those predicted for stellar populations with the observed spatial structure orbiting within the most massive 'satellite' substructures in our simulations. Less massive substructures have weaker potential wells than those hosting the observed satellites. If there is a halo substructure 'problem', it consists of understanding why halo substructures have been so inefficient in making stars. Suggested modifications of dark matter properties (for example, self-interacting or warm dark matter) may well spoil the good agreement found for standard cold dark matter.
2002
Article
http://edoc.mpg.de/10795
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.335, L84-L88 (2002)
en
oai:edoc.mpg.de:108062006-10-1625:114
The phase-space structure of a dark-matter halo: Implications for dark-matter direct detection experiments
Helmi, A.
White, S. D. M.
Springel, V.
We study the phase-space structure of a dark-matter halo formed in a high resolution simulation of a LambdaCDM cosmology. Our goal is to quantify how much substructure is left over from the inhomogeneous growth of the halo, and how it may affect the signal in experiments aimed at detecting the dark matter particles directly. If we focus on the equivalent of "solar vicinity," we find that the dark matter is smoothly distributed in space. The probability of detecting particles bound within dense lumps of individual mass less than 10(7) M(circle dot)h(- 1) is small, less than 10(-2). The velocity ellipsoid in the solar neighborhood deviates only slightly from a multivariate Gaussian, and can be thought of as a superposition of thousands of kinematically cold streams. The motions of the most energetic particles are, however, strongly clumped and highly anisotropic. We conclude that experiments may safely assume a smooth multivariate Gaussian distribution to represent the kinematics of dark-matter particles in the solar neighborhood. Experiments sensitive to the direction of motion of the incident particles could exploit the expected anisotropy to learn about the recent merging history of our Galaxy.
2002
Article
http://edoc.mpg.de/10806
urn:ISSN:0556-2821
Physical Review D, v.66, 063502-1-063502-11 (2002)
en
oai:edoc.mpg.de:108122006-10-1625:114
The abundance and clustering of dark haloes in the standard Lambda CDM cosmogony
Mo, H. J.
White, S. D. M.
galaxies : clusters : general; galaxies : formation; cosmology : theory; dark matter; large-scale structure of Universe
Much evidence suggests that we live in a flat cold dark matter universe with a cosmological constant. Accurate analytic formulae are now available for many properties of the dark halo population in such a Universe. Assuming current 'concordance' values for the cosmological parameters, we plot halo abundance against redshift as a function of halo mass, halo temperature, the fraction of cosmic matter in haloes, halo clustering strength, and the clustering strength of the z = 0 descendants of high-redshift haloes. These plots are useful for understanding how nonlinear structure grows in the model. They demonstrate a number of properties that may seem surprising, for example: 10(9) M.haloes are as abundant at z = 20 as L-* galaxies are today; 10(6) K haloes are equally abundant at z = 8 and at z = 0; 10 per cent of all matter is currently in haloes hotter than 1 keV, while more than half is in haloes too cool to trap photo-ionized gas; 1 per cent of all matter at z = 15 is in haloes hot enough to ionize hydrogen; haloes of given mass or temperature are more clustered at higher redshift; haloes with the abundance of present-day L-* galaxies are equally clustered at all z < 20; the metals produced by star- formation at z > 10 are more clustered at z = 0 than are L-* galaxies.
2002
Article
http://edoc.mpg.de/10812
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.336, 112-118 (2002)
en
oai:edoc.mpg.de:108182006-10-1625:114
Cosmological smoothed particle hydrodynamics simulations: the entropy equation
Springel, V.
Hernquist, L.
methods : numerical; galaxies : evolution; galaxies : starburst
We discuss differences in simulation results that arise between the use of either the thermal energy or the entropy as an independent variable in smoothed particle hydrodynamics (SPH). In this context, we derive a new version of SPH that, when appropriate, manifestly conserves both energy and entropy if smoothing lengths are allowed to adapt freely to the local mass resolution. To test various formulations of SPH, we consider point-like energy injection, as in certain models of supernova feedback, and find that powerful explosions are well represented by SPH even when the energy is deposited into a single particle, provided that the entropy equation is integrated. If the thermal energy is instead used as an independent variable, unphysical solutions can be obtained for this problem. We also examine the radiative cooling of gas spheres that collapse and virialize in isolation, and of haloes that form in cosmological simulations of structure formation. When applied to these problems, the thermal energy version of SPH leads to substantial overcooling in haloes that are resolved with up to a few thousand particles, while the entropy formulation is biased only moderately low for these haloes under the same circumstances. For objects resolved with much larger particle numbers, the two approaches yield consistent results. We trace the origin of the differences to systematic resolution effects in the outer parts of cooling flows. When the thermal energy equation is integrated and the resolution is low, the compressional heating of the gas in the inflow region is underestimated, violating entropy conservation and improperly accelerating cooling. The cumulative effect of this overcooling can be significant. In cosmological simulations of moderate size, we find that the fraction of baryons which cool and condense can be reduced by up to a factor similar to2 if the entropy equation is employed rather than the thermal energy equation, partly explaining discrepancies with semi-analytic treatments of galaxy formation. We also demonstrate that the entropy method leads to a greatly reduced scatter in the density-temperature relation of the low-density Lyalpha forest relative to the thermal energy approach, in accord with theoretical expectations.
2002
Article
http://edoc.mpg.de/10818
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.333, 649-664 (2002)
en
oai:edoc.mpg.de:108462006-10-1625:114
Mapping the galactic halo today and in the future
Helmi, A.
EDP Sciences
2002 EDP Sciences
2002
Conference-Paper
http://edoc.mpg.de/10846
urn:ISBN:2-86883-597-X
Bienayme, O.; Turon, C.: GAIA : a European space project, EDP Sciences, 273-275 (2002)
oai:edoc.mpg.de:109422006-10-1625:114
Analysis of two-point statistics of cosmic shear - I. Estimators and covariances
Schneider, P.
van Waerbeke, L.
Kilbinger, M.
Mellier, Y.
dark matter; gravitational lensing; large-scale structure of the Universe
Recently, cosmic shear, the weak lensing effect by the inhomogeneous matter distribution in the Universe, has not only been detected by several groups, but the observational results have been used to derive constraints on cosmological parameters. For this purpose, several cosmic shear statistics have been employed. As shown recently, all second-order statistical measures can be expressed in terms of the two-point correlation functions of the shear, which thus represents the basic quantity; also, from a practical point-of-view, the two- point correlation functions are easiest to obtain from observational data which typically have complicated geometry. We derive in this paper expressions for the covariance matrix of the cosmic shear two-point correlation functions which are readily applied to any survey geometry. Furthermore, we consider the more special case of a simple survey geometry which allows us to obtain approximations for the covariance matrix in terms of integrals which are readily evaluated numerically. These results are then used to study the covariance of the aperture mass dispersion which has been employed earlier in quantitative cosmic shear analyses. We show that the aperture mass dispersion, measured at two different angular scales, quickly decorrelates with the ratio of the scales. Inverting the relation between the shear two-point correlation functions and the power spectrum of the underlying projected matter distribution, we construct estimators for the power spectrum and for the band powers, and show that they yields accurate approximations; in particular, the correlation between band powers at different wave numbers is quite weak. The covariance matrix of the shear correlation function is then used to investigate the expected accuracy of cosmological parameter estimates from cosmic shear surveys. Depending on the use of prior information, e.g. from CMB measurements, cosmic shear can yield very accurate determinations of several cosmological parameters, in particular the normalization sigma(8) of the power spectrum of the matter distribution, the matter density parameter Omega(m), and the shape parameter Gamma.
2002
Article
http://edoc.mpg.de/10942
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.396, 1-19 (2002)
en
oai:edoc.mpg.de:109432006-10-1625:114
Predicting the clustering properties of galaxy clusters detectable by the Planck satellite
Moscardini, L.
Bartelmann, M.
Matarrese, S.
Andreani, P.
galaxies : clusters : general; cosmic microwave background; cosmology : theory; dark matter; large-scale structure of Universe
We study the clustering properties of the galaxy clusters detectable by the Planck satellite owing to their thermal Sunyaev-Zel'dovich (SZ) effect. We take the past light-cone effect and the redshift evolution of both the underlying dark matter correlation function and the cluster bias factor into account. A theoretical mass-temperature relation allows us to convert the sensitivity limit of a catalogue into a minimum mass for the dark matter haloes hosting the clusters. We confirm that the correlation length is an increasing function of the sensitivity limits defining the survey. Using the expected characteristics of the Planck cluster catalogue, which will be a quite large and unbiased sample, we predict the two- point correlation function and power spectrum for different cosmological models. We show that the wide redshift distribution of the Planck survey will allow us to constrain the cluster clustering properties up to z approximate to 1. The dependence of our results on the main cosmological parameters (the matter density parameter, the cosmological constant and the normalization of the density power spectrum) is extensively discussed. We find that future Planck clustering data will place only mild constraints on the cosmological parameters, because the results depend on the physical characteristics of the intracluster medium, like the baryon fraction and the mass- temperature relation. Once the cosmological model and the Hubble constant are determined, the clustering data will allow a determination of the baryon fraction with an accuracy of a few per cent.
2002
Article
http://edoc.mpg.de/10943
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.335, 984-992 (2002)
en
oai:edoc.mpg.de:109512006-10-1625:114
Signatures of galaxy mergers in the Milky Way: Here, there and everywhere
Helmi, A.
The hierarchical paradigm predicts that large galaxies like the Milky Way formed through mergers of smaller systems, which are expected to leave behind substructures in the halo of the final product. Recently the first tests of this prediction on galaxies other than the Milky Way have been made (eg NGC 5907 by Sackett et al.; M31 by Ibata et al.), but one should bare in mind that it is extremely difficult to detect halos in external galaxies let alone substructures in those halos. On the other hand, the multi-dimensional phase-space information available for our Galaxy (6d for stars in the vicinity of the Sun, and 4d for more distant ones) enables us to directly search for merger signatures.
2002
Conference-Paper
http://edoc.mpg.de/10951
urn:ISSN:0004-640X
Astrophysics and Space Science, v.281, 1-2, 351-354 (2002)
en
oai:edoc.mpg.de:109542006-10-1625:114
The clustering of galaxies around quasars
Kauffmann, G.
Haehnelt, M. G.
black hole physics; galaxies : formation; galaxies : nuclei; quasars : general
We study the cross-correlation between quasars and galaxies by embedding models for the formation and evolution of the two populations in cosmological N -body simulations. We adopt the quasar evolution model of Kauffmann & Haehnelt, in which supermassive black holes are formed and fuelled during major mergers. We define the 'bias' parameter b(QG) as the ratio of the cross-correlation function xi(QG) to the galaxy autocorrelation function xi(GG) . On scales larger than 1 h(-1) Mpc, the values of b(QG) predicted by our models at low redshift depend very little on galaxy selection. They measure the characteristic mass of the dark matter haloes that host quasars and can be used to estimate the typical quasar lifetime. In current redshift surveys, such measurements will constrain the lifetimes of low-redshift quasars more accurately than measurements of the quasar autocorrelation function, because galaxies have much higher space densities than quasars. On scales smaller than 1 h(-1) Mpc, the main contribution to xi(QG) comes from quasar/galaxy pairs in the same dark matter halo. The amplitude of xi(QG) depends both on the location of the host galaxy and on the density profile of other galaxies within the halo. As a result, measurements on these scales yield information about the processes responsible for fuelling supermassive black holes. At high redshifts our models predict that quasars of fixed luminosity are located in less massive haloes than at low redshift. They are therefore less biased relative to galaxies of given luminosity or stellar mass. We have used the simulations to calculate the evolution of the quasar autocorrelation function. We find that models with quasar lifetimes in the range 10(6)-10(7) yr provide a good match to the results of the 2dF QSO survey.
2002
Article
http://edoc.mpg.de/10954
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.332, 529-535 (2002)
en
oai:edoc.mpg.de:109632006-10-1625:114
Gravitational lensing of extended high-redshift sources by dark matter haloes
Perrotta, F.
Baccigalupi, C.
Bartelmann, M.
De Zotti, G.
Granato, G. L.
gravitational lensing; galaxies : haloes
High-redshift galaxies and quasi-stellar objects (QSOs) are most likely to be strongly lensed by intervening haloes between the source and the observer. In addition, a large fraction of lensed sources is expected to be seen in the submillimetre region, as a result of the enhanced magnification bias on the steep intrinsic number counts. We extend in three directions Blain's earlier study of this effect. First, we use a modification of the Press-Schechter mass function and detailed lens models to compute the magnification probability distribution. We compare the magnification cross-sections of populations of singular isothermal spheres and Navarro, Frenk & White (NFW) haloes and find that they are very similar, in contrast to the image-splitting statistics which were recently investigated in other studies. The distinction between the two types of density profile is therefore, irrelevant for our purposes. Secondly, we discuss quantitatively the maximum magnification, mu(max), that can be achieved for extended sources (galaxies) with realistic luminosity profiles, taking into account the possible ellipticity, of the lensing potential. We find that mu(max) plausibly falls into the range 10-30 for sources of 1-10 h(-1) kpc effective radius at redshifts within 1-4. Thirdly, we apply our model for the lensing magnification to a class of sources following the luminosity, evolution typical for a unified scheme of QSO formation. As a result of the peculiar steepness of their intrinsic number counts, we find that the lensed source counts at a fiducial wave length of 850 mum can exceed the unlensed counts by several orders of magnitude at flux densities greater than or similar to100 mJy, even with a conservative choice of the maximum magnification.
2002
Article
http://edoc.mpg.de/10963
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.329, 445-455 (2002)
en
oai:edoc.mpg.de:109652006-10-1625:114
Probing the intergalactic medium with the Ly alpha forest along multiple lines of sight to distant QSOs
Viel, M.
Matarrese, S.
Mo, H. J.
Haehnelt, M. G.
Theuns, T.
intergalactic medium; quasars : absorption lines; cosmology : theory; large-scale structure of Universe
We present an effective implementation of analytical calculations of the Lyalpha opacity distribution of the intergalactic medium (IGM) along multiple lines of sight (LOS) to distant quasars in a cosmological setting. The method assumes that the distribution of neutral hydrogen follows that of an underlying dark matter density field, and that the density distribution is a (local) lognormal distribution. It fully accounts for the expected correlations between LOS and the cosmic variance in the large-scale modes of the dark matter distribution. Strong correlations extending up to similar to300 kpc (proper) and more are found at redshifts z similar to 2-3, in agreement with observations. These correlations are investigated using the cross-correlation coefficient and the cross-power spectrum of the flux distribution along different LOS, and by identifying coincident absorption features as fitted with a Voigt profile fitting routine. The cross- correlation coefficient between the LOS can be used to constrain the shape-parameter Gamma of the power spectrum if the temperature and the temperature density relation of the IGM can be determined independently. We also propose a new technique to recover the 3D linear dark matter power spectrum by integrating over 1D flux cross-spectra, which is complementary to the usual 'differentiation' of 1D auto- spectra. The cross-power spectrum suffers much less from errors uncorrelated in different LOS, like those introduced by continuum fitting. Investigations of the flux correlations in adjacent LOS should thus allow us to extend studies of the dark matter power spectrum with the Lyalpha forest to significantly larger scales than is possible with flux auto-power spectra. 30 pairs with separations of 1-2 arcmin should be sufficient to determine the 1D cross-spectrum at scales of 60 h(-1) Mpc with an accuracy of about 30 per cent (corresponding to a 15 per cent error of the rms density fluctuation amplitude) if the error is dominated by cosmic variance.
2002
Article
http://edoc.mpg.de/10965
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.329, 848-862 (2002)
en
oai:edoc.mpg.de:109712006-10-1625:114
All-sky astrophysical component separation with fast independent component analysis (FASTICA)
Maino, D.
Farusi, A.
Baccigalupi, C.
Perrotta, F.
Banday, A. J.
Bedini, L.
Burigana, C.
De Zotti, G.
Gorski, K. M.
Salerno, E.
methods : data analysis; techniques : image processing; cosmic microwave background
We present a new, fast, algorithm for the separation of astrophysical components superposed in maps of the sky. The algorithm, based on the Independent Component Analysis (ICA) technique, is aimed at recovering both the spatial pattern and the frequency scalings of the emissions from statistically independent astrophysical processes, present along the line-of- sight, from multi-frequency observations, without any a priori assumption on properties of the components to be separated, except that all of them, except possibly one, must have non- Gaussian distributions. The analysis starts from very simple toy-models of the sky emission in order to assess the quality of the reconstruction when inputs are well known and controlled. In particular, we study the dependence of the results of separation conducted on and off the Galactic plane independently, showing that optimal separation is achieved for sky regions where components are smoothly distributed. Then we consider simulated observations of the microwave sky with angular resolution and instrumental noise, supposed to be white and stationary, at the mean nominal levels for the Planck satellite. The angular response function is assumed to be identical at each frequency since this is, up to now, one of the Fast Independent Component Analysis (FastICA) limitations. We consider several Planck observation channels containing the most important known diffuse signals: the cosmic microwave background (CMB), Galactic synchrotron, dust and free-free emissions. A method for calibrating the reconstructed maps of each component at each frequency has been devised. The spatial patterns of all the components have been recovered on all scales probed by the instrument. In particular, the CMB angular power spectra is recovered at the per cent level up to l(max) similar or equal to2000. Frequency scalings and normalization have been recovered with better than 1 per cent precision for all the components at frequencies and in sky regions where their signal-to-noise ratio greater than or similar to1.5; the error increases at similar to10 per cent level for signal-to- noise ratios similar or equal to1. Runs have been performed on a Pentium III 600-MHz computer; although the computing time slightly depends on the number of channels and components to be recovered, FastICA typically took about 10 min for all-sky simulations with 3.5-arcmin pixel size. Although the quoted results have been obtained under a number of simplifying assumptions, we conclude that FastICA is an extremely promising technique for analysing the maps that will be obtained by the forthcoming high-resolution CMB experiments.
2002
Article
http://edoc.mpg.de/10971
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.334, 53-68 (2002)
en
oai:edoc.mpg.de:109742006-10-1625:114
Star formation, metallicity and dust properties derived from the Stromlo-APM galaxy survey spectra
Charlot, S.
Kauffmann, G.
Longhetti, M.
Tresse, L.
White, S. D. M.
Maddox, S. J.
Fall, S. M.
galaxies : general; galaxies : ISM; galaxies : stellar content
We have derived star formation rates (SFRs), gas-phase oxygen abundances and effective dust absorption optical depths for a sample of galaxies drawn from the Stromlo-APM redshift survey using the new model of Charlot & Longhetti (CLO1), which provides a physically consistent description of the effects of stars, gas and dust on the integrated spectra of galaxies. Our sample consists of 705 galaxies with measurements of the fluxes and equivalent widths of Halpha, [O II] and one or both of [N II] and [S II]. For a subset of the galaxies, 60- and 100-mum IRAS fluxes are available. We compare the star formation rates derived using the model with those derived using standard estimators based on the Halpha, the [O II] and the far-infrared luminosities of the galaxies. The CL01 SFR estimates agree well with those derived from the IRAS fluxes, but are typically a factor of similar to3 higher than those derived from the Halpha or the [O II] fluxes, even after the usual mean attenuation correction of A(Halpha) = 1 mag is applied to the data. We show that the reason for this discrepancy is that the standard Halpha estimator neglects the absorption of ionizing photons by dust in H II regions and the contamination of Halpha emission by stellar absorption. We also use our sample to study variations in star formation and metallicity as a function of galaxy absolute b(J) magnitude. For this sample, the star formation rate per unit b(J) luminosity is independent of magnitude. The gas-phase oxygen abundance does increase with b(J) luminosity, although the scatter in metallicity at fixed magnitude is large.
2002
Article
http://edoc.mpg.de/10974
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.330, 876-888 (2002)
en
oai:edoc.mpg.de:109752006-10-1625:114
On the distribution of haloes, galaxies and mass
Casas-Miranda, R.
Mo, H. J.
Sheth, R. K.
Börner, G.
galaxies : clusters : general; galaxies : formation; cosmology : theory; dark matter
The stochasticity in the distribution of dark haloes in the cosmic density field is reflected in the distribution function P-V (N (h) \delta (m) ), which gives the probability of finding N (h) haloes in a volume V with mass density contrast delta (m) . We study the properties of this function using high- resolution N -body simulations, and find that P-V (N (h) \delta (m) ) is significantly non-Poisson. The ratio between the variance and the mean goes from similar to1 (Poisson) at 1+delta (m) <<1 to <1 (sub-Poisson) at 1+delta (m) similar to1< to >1 (super-Poisson) at 1+δ (m) >>1. The mean bias relation is found to be well described by halo bias models based on the Press-Schechter formalism. The sub-Poisson variance can be explained as a result of halo exclusion, while the super-Poisson variance at high delta (m) may be explained as a result of halo clustering. A simple phenomenological model is proposed to describe the behaviour of the variance as a function of delta (m) . Galaxy distribution in the cosmic density field predicted by semi-analytic models of galaxy formation shows similar stochastic behaviour. We discuss the implications of the stochasticity in halo bias to the modelling of higher order moments of dark haloes and of galaxies.
2002
Article
http://edoc.mpg.de/10975
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.333, 730-738 (2002)
en
oai:edoc.mpg.de:109772006-10-1625:114
Galaxy clustering in early Sloan Digital Sky Survey redshift data
Zehavi, I.
Blanton, M. R.
Frieman, J. A.
Weinberg, D. H.
Mo, H. J.
Strauss, M. A.
Anderson, S. F.
Annis, J.
Bahcall, N. A.
Bernardi, M.
Briggs, J. W.
Brinkmann, J.
Burles, S.
Carey, L.
Castander, F. J.
Connolly, A. J.
Csabai, I.
Dalcanton, J. J.
Dodelson, S.
Doi, M.
Eisenstein, D.
Evans, M. L.
Finkbeiner, D. P.
Friedman, S.
Fukugita, M.
Gunn, J. E.
Hennessy, G. S.
Hindsley, R. B.
Ivezic, Z.
Kent, S.
Knapp, G. R.
Kron, R.
Kunszt, P.
Lamb, D. Q.
Leger, R. F.
Long, D. C.
Loveday, J.
Lupton, R. H.
McKay, T.
Meiksin, A.
Merrelli, A.
Munn, J. A.
Narayanan, V.
Newcomb, M.
Nichol, R. C.
Owen, R.
Peoples, J.
Pope, A.
Rockosi, C. M.
Schlegel, D.
Schneider, D. P.
Scoccimarro, R.
Sheth, R. K.
Siegmund, W.
Smee, S.
Snir, Y.
Stebbins, A.
Stoughton, C.
SubbaRao, M.
Szalay, A. S.
Szapudi, I.
Tegmark, M.
Tucker, D. L.
Uomoto, A.
Berk, D. V.
Vogeley, M. S.
Waddell, P.
Yanny, B.
York, D. G.
cosmology : observations; cosmology : theory; dark matter; galaxies : clusters : general; galaxies : distances and redshifts; large-scale structure of universe
We present the first measurements of clustering in the Sloan Digital Sky Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies with redshifts 5700 km s(-1) less than or equal to cz less than or equal to 39, 000 km s(-1), distributed in several long but narrow (2.degrees5-5degrees) segments, covering 690 deg(2). For the full, flux-limited sample, the redshift-space correlation length is approximately 8 h(-1) Mpc. The two-dimensional correlation function xi(r(p), pi) shows clear signatures of both the small-scale, "fingers- of-God" distortion caused by velocity dispersions in collapsed objects and the large-scale compression caused by coherent flows, though the latter cannot be measured with high precision in the present sample. The inferred real-space correlation function is well described by a power law, xi(r) = (r/6.1 +/- 0.2 h(-1) Mpc)(-1.75 +/- 0.03), for 0.1 h(-1) Mpc less than or equal to r less than or equal to 16 h(-1) Mpc. The galaxy pair- wise velocity dispersion is sigma(12) approximate to 600 +/- 100 km s(-1) for projected separations 0.15 h(-1) Mpc less than or equal to r(p) less than or equal to5 h(-1) Mpc. When we divide the sample by color, the red galaxies exhibit a stronger and steeper real-space correlation function and a higher pairwise velocity dispersion than do the blue galaxies. The relative behavior of subsamples defined by high/low profile concentration or high/low surface brightness is qualitatively similar to that of the red/blue subsamples. Our most striking result is a clear measurement of scale-independent luminosity bias at r less than or similar to 10 h(-1) Mpc: subsamples with absolute magnitude ranges centered on M-* - 1.5, M-*, and M-* + 1.5 have real-space correlation functions that are parallel power laws of slope approximate to -1.8 with correlation lengths of approximately 7.4, 6.3, and 4.7 h(-1) Mpc, respectively.
2002
Article
http://edoc.mpg.de/10977
urn:ISSN:0004-637X
The Astrophysical Journal, v.571, 172-190 (2002)
en
oai:edoc.mpg.de:109782011-02-1125:114
Sloan digital sky survey: early data release
Stoughton, C.
Lupton, R. H.
Bernardi, M.
Blanton, M. R.
Burles, S.
Castander, F. J.
Connolly, A. J.
Eisenstein, D. J.
Frieman, J. A.
Hennessy, G. S.
Hindsley, R. B.
Ivezic, Z.
Kent, S.
Kunszt, P. Z.
Lee, B. C.
Meiksin, A.
Munn, J. A.
Newberg, H. J.
Nichol, R. C.
Nicinski, T.
Pier, J. R.
Richards, G. T.
Richmond, M. W.
Schlegel, D. J.
Smith, J. A.
Strauss, M. A.
SubbaRao, M.
Szalay, A. S.
Thakar, A. R.
Tucker, D. L.
Vanden Berk, D. E.
Yanny, B.
Adelman, J. K.
Anderson, J. E.
Anderson, S. F.
Annis, J.
Bahcall, N. A.
Bakken, J. A.
Bartelmann, M.
Bastian, S.
Bauer, A.
Berman, E.
Böhringer, H.
Boroski, W. N.
Bracker, S.
Briegel, C.
Briggs, J. W.
Brinkmann, J.
Brunner, R.
Carey, L.
Carr, M. A.
Chen, B.
Christian, D.
Colestock, P. L.
Crocker, J. H.
Csabai, I. N.
Czarapata, P. C.
Dalcanton, J.
Davidsen, A. F.
Davis, J. E.
Dehnen, W.
Dodelson, S.
Doi, M.
Dombeck, T.
Donahue, M.
Ellman, N.
Elms, B. R.
Evans, M. L.
Eyer, L.
Fan, X. H.
Federwitz, G. R.
Friedman, S.
Fukugita, M.
Gal, R.
Gillespie, B.
Glazebrook, K.
Gray, J.
Grebel, E. K.
Greenawalt, B.
Greene, G.
Gunn, J. E.
de Haas, E.
Haiman, Z.
Haldeman, M.
Hall, P. B.
Hamabe, M.
Hansen, B.
Harris, F. H.
Harris, H.
Harvanek, M.
Hawley, S. L.
Hayes, J. J. E.
Heckman, T. M.
Helmi, A.
Henden, A.
Hogan, C. J.
Hogg, D. W.
Holmgren, D. J.
Holtzman, J.
Huang, C. H.
Hull, C.
Ichikawa, S. I.
Ichikawa, T.
Johnston, D. E.
Kauffmann, G.
Kim, R. S. J.
Kimball, T.
Kinney, E.
Klaene, M.
Kleinman, S. J.
Klypin, A.
Knapp, G. R.
Korienek, J.
Krolik, J.
Kron, R. G.
Krzesinski, J.
Lamb, D. Q.
Leger, R. F.
Limmongkol, S.
Lindenmeyer, C.
Long, D. C.
Loomis, C.
Loveday, J.
MacKinnon, B.
Mannery, E. J.
Mantsch, P. M.
Margon, B.
McG'hee, P.
Mckay, T. A.
McLean, B.
Menou, K.
Merelli, A.
Mo, H. J.
Monet, D. G.
Nakamura, O.
Narayanan, V. K.
Nash, T.
Neilsen, E. H.
Newman, P. R.
Nitta, A.
Odenkirchen, M.
Okada, N.
Okamura, S.
Ostriker, J. P.
Owen, R.
Pauls, A. G.
Peoples, J.
Peterson, R. S.
Petravick, D.
Pope, A.
Pordes, R.
Postman, M.
Prosapio, A.
Quinn, T. R.
Rechenmacher, R.
Rivetta, C. H.
Rix, H. W.
Rockosi, C. M.
Rosner, R.
Ruthmansdorfer, K.
Sandford, D.
Schneider, D. P.
Scranton, R.
Sekiguchi, M.
Sergey, G.
Sheth, R.
Shimasaku, K.
Smee, S.
Snedden, S. A.
Stebbins, A.
Stubbs, C.
Szapudi, I.
Szkody, P.
Szokoly, G. P.
Tabachnik, S.
Tsvetanov, Z.
Uomoto, A.
Vogeley, M. S.
Voges, W.
Waddell, P.
Walterbos, R.
Wang, S. I.
Watanabe, M.
Weinberg, D. H.
White, R. L.
White, S. D. M.
Wilhite, B.
Wolfe, D.
Yasuda, N.
York, D. G.
Zehavi, I.
Zheng, W.
atlases; catalogs; surveys
The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of 10 6 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg(2) of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux- and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Angstrom at R approximate to 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.
2002
Article
http://edoc.mpg.de/10978
urn:ISSN:0004-6256
Astronomical Journal, v.123, 485-548 (2002)
en
oai:edoc.mpg.de:109812006-10-1625:114
Dynamics of ejection from galaxies and the variable mass hypothesis
Narlikar, J. V.
Vishwakarma, R. G.
Banerjee, S. K.
Das, P. K.
Arp, H. C.
Increasing numbers of active galaxies with significant alignments of quasars are being observed. It is the purpose of this paper to explore ejection dynamics of these quasars using the variable mass hypothesis (VMH) originally discussed by Narlikar and Das in 1980. According to the VMH quasars are ejected from parent galaxies initially with zero rest mass which grows through a Machian interaction. The intrinsic redshift of the quasar steadily decreases as its mass grows, but always remains in excess of the redshift of the galaxy. The ultimate aim of this hypothesis is to quantitatively relate the observed ordering of redshifts of ejected quasars, with separation from the galaxy, their intrinsic redshifts and the age of the evolutionary stage of the ejecta.
2002
Article
http://edoc.mpg.de/10981
urn:ISSN:0218-2718
International Journal of Modern Physics D, v.11, 245-257 (2002)
en
oai:edoc.mpg.de:109892011-03-1825:114
The fundamental plane of spiral galaxies: theoretical expectations
Shen, S. Y.
Mo, H. J.
Shu, C. G.
galaxies : formation; galaxies : fundamental parameters; galaxies : spiral; galaxies : structure
Current theory of disc galaxy formation is used to study fundamental-plane (FP) type of relations for disc galaxies. We examine how the changes in model parameters affect these relations and explore the possibility of using such relations to constrain theoretical models. The distribution of galaxy discs in the space of their fundamental properties are predicted to be concentrated in a plane, with the Tully-Fisher (TF) relation (a relation between luminosity L and maximum rotation velocity V-m) being an almost edge-on view. Using rotation velocities at larger radii generally leads to larger TF scatter. In searching for a third parameter, we find that both the disc scalelength R-d (or surface brightness) and the rotation-curve shape are correlated with the TF scatter. The FP relation in the (log L, log V-m, log R-d)-space obtained from the theory is L proportional to R-d(alpha') V-m(beta'), with alpha' similar to 0.50 and beta' similar to 2.60, consistent with the preliminary result we obtain from observational data. Using the isophotal radius instead of R-d leads to higher alpha', lower beta' and smaller scatter. Among the model parameters we probe, variation in any of them can generate significant scatter in the TF relation, but the effects of the spin parameter and halo concentration can be reduced significantly by introducing R-d While the scatter caused by varying m(d) (the ratio between disc mass and halo mass) is most effectively reduced by introducing the parameters which describe the rotation-curve shape. The TF and FP relations combined should therefore provide useful constraints on models of galaxy formation.
2002
Article
http://edoc.mpg.de/10989
info:doi/10.1046/j.1365-8711.2002.05187.x
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.331, 259-272 (2002)
en
oai:edoc.mpg.de:109902006-10-1625:114
Are there MACHOs in the Milky Way halo?
Green, A. M.
Jedamzik, K.
Galaxy : halo; cosmology : dark matter
Microlensing searches aim to detect compact halo dark matter via its gravitational lensing effect on stars within the Large Magellanic Cloud. These searches have led to the claim that roughly one fifth of the galactic halo dark matter may be in the form of compact, solar-mass objects. We analyze this hypothesis by considering the goodness-of-fit of the best-fit halo dark matter solutions to the observational data. We show that the distribution of the durations of the observed microlensing events is significantly narrower than that expected to result from a standard halo lens population at 90 to 95% confidence, casting doubt on the lenses constituting halo dark matter. This conclusion may possibly be avoided if (i) the Milky Way halo is sufficiently nonstandard or (ii) a large fraction of the events are due to non-halo populations with event durations coincidentally close to those of the putative halo population or (iii) individual event durations have been seriously underestimated due to blending.
2002
Article
http://edoc.mpg.de/10990
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.395, 31-35 (2002)
en
oai:edoc.mpg.de:109922006-10-1625:114
Simulating the formation of the local galaxy population
Mathis, H.
Lemson, G.
Springel, V.
Kauffmann, G.
White, S. D. M.
Eldar, A.
Dekel, A.
galaxies : clusters : general; galaxies : formation; large- scale structure of Universe
We simulate the formation and evolution of the local galaxy population, starting from initial conditions with a smoothed linear density field which matches that derived from the IRAS 1.2-Jy galaxy survey. Our simulations track the formation and evolution of all dark matter haloes more massive than 10(11) M- . out to a distance of 8000 km s(-1) from the Milky Way. We implement prescriptions similar to those of Kauffmann et al. to follow the assembly and evolution of the galaxies within these haloes. We focus on two variants of the CDM cosmology: a LambdaCDM model and a tau CDM model. Galaxy formation in each is adjusted to reproduce the I -band Tully-Fisher relation of Giovanelli et al. We compare the present-day luminosity functions, colours, morphology and spatial distribution of our simulated galaxies with those of the real local population, in particular with the Updated Zwicky Catalog, with the IRAS PSCz redshift survey, and with individual local clusters such as Coma, Virgo and Perseus. We also use the simulations to study the clustering bias between the dark matter and galaxies of differing type. Although some significant discrepancies remain, our simulations recover the observed intrinsic properties and the observed spatial distribution of local galaxies reasonably well. They can thus be used to calibrate methods which use the observed local galaxy population to estimate the cosmic density parameter or to draw conclusions about the mechanisms of galaxy formation. To facilitate such work, we publicly release our z =0 galaxy catalogues, together with the underlying mass distribution.
2002
Article
http://edoc.mpg.de/10992
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.333, 739-762 (2002)
en
oai:edoc.mpg.de:109932006-10-1625:114
Gravitational microlensing events due to stellar-mass black holes
Bennett, D. P.
Becker, A. C.
Quinn, J. L.
Tomaney, A. B.
Alcock, C.
Allsman, R. A.
Alves, D. R.
Axelrod, T. S.
Calitz, J. J.
Cook, K. H.
Drake, A. J.
Fragile, P. C.
Freeman, K. C.
Geha, M.
Griest, K.
Johnson, B. R.
Keller, S. C.
Laws, C.
Lehner, M. J.
Marshall, S. L.
Minniti, D.
Nelson, C. A.
Peterson, B. A.
Popowski, P.
Pratt, M. R.
Quinn, P. J.
Rhie, S. H.
Stubbs, C. W.
Sutherland, W.
Vandehei, T.
Welch, D.
Galaxy : bulge; gravitational lensing
We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find six events that exhibit very strong microlensing parallax signals due, in part, to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distances and masses of the lens objects based on a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are greater than 1 M-circle dot, which suggests that a substantial fraction of the Galactic lenses may be massive stellar remnants. This could explain the observed excess of long-timescale microlensing events. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M/M-circle dot = 6(-3)(+10) and M/M-circle dot = 6(-3)(+7), respectively. The observed upper limits on the absolute brightness of main-sequence stars for these lenses are less than 1 L-circle dot, so both lenses are black hole candidates. The black hole interpretation is also favored by a likelihood analysis with a Bayesian prior using a conventional model for the lens mass function. We consider the possibility that the source stars for some of these six events may lie in the foreground Galactic disk or in the Sagittarius (Sgr) dwarf galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future Hubble Space Telescope observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by the Space Interferometry Mission or the Keck or VLT interferometers, as explained by Delplancke, Gorski, & Richichi, will allow direct measurements of the lens masses for stellar remnant lenses as well.
2002
Article
http://edoc.mpg.de/10993
urn:ISSN:0004-637X
The Astrophysical Journal, v.579, 639-659 (2002)
en
oai:edoc.mpg.de:121232006-10-1625:114
Galaxy cores as relics of black hole mergers
Milosavljevic, M.
Merritt, D.
Rest, A.
van den Bosch, F. C.
black hole physics; galaxies : elliptical and lenticular; cD; galaxies : interactions; galaxies : nuclei
We investigate the hypothesis that the cores of elliptical galaxies and bulges are created from the binding energy liberated by the coalescence of supermassive binary black holes during galaxy mergers. Assuming that the central density profiles of galaxies were initially steep power laws, rho similar to r(-2), we define the 'mass deficit' as the mass in stars that had to be removed from the nucleus in order to produce the observed core. We use non-parametric deprojection to compute the mass deficit in a sample of 35 early-type galaxies with high-resolution imaging data. We find that the mass deficit correlates well with the mass of the nuclear black hole, consistent with the predictions of merger models. We argue that cores in haloes of non-interacting dark matter particles should be comparable in size to those observed in the stars.
2002
Article
http://edoc.mpg.de/12123
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.331, L51-L55 (2002)
en
oai:edoc.mpg.de:121362006-10-1625:114
Measurement of the cosmic microwave background bispectrum on the COBE DMR sky maps
Komatsu, E.
Wandelt, B. D.
Spergel, D. N.
Banday, A. J.
Gorski, K. M.
cosmic microwave background; cosmology : observations; early universe
We measure the angular bispectrum of the cosmic microwave background (CMB) radiation anisotropy from the COBE Differential Microwave Radiometer (DMR) 4 yr sky maps. The angular bispectrum is the harmonic transform of the three-point correlation function, analogous to the angular power spectrum, the harmonic transform of the two-point correlation function. First, we study statistical properties of the bispectrum and the normalized bispectrum. We find the latter more useful for statistical analysis; the distribution of the normalized bispectrum is very much Gaussian, while the bare bispectrum distribution is highly non-Gaussian. Then, we measure 466 modes of the normalized bispectrum, all independent combinations of three-point configurations up to a maximum multipole of 20, the mode corresponding to the DMR beam size. By measuring 10 times as many modes as the sum of previous work, we test the Gaussianity of the DMR maps. We compare the data with the simulated Gaussian realizations, finding no significant detection of the normalized bispectrum on a mode-by-mode basis. We also find that the previously reported detection of the normalized bispectrum is consistent with a statistical fluctuation. By fitting a theoretical prediction to the data for the primordial CMB bispectrum, which is motivated by slow- roll inflation, we put a weak constraint on the parameter characterizing nonlinearity in inflation. Simultaneously fitting the foreground bispectra estimated from interstellar dust and synchrotron template maps shows that neither dust nor synchrotron emission significantly contributes to the bispectrum at high Galactic latitude. We conclude that the DMR map is consistent with Gaussianity.
2002
Article
http://edoc.mpg.de/12136
urn:ISSN:0004-637X
The Astrophysical Journal, v.566, 19-29 (2002)
en
oai:edoc.mpg.de:121382006-10-1625:114
Galaxy clusters in Hubble volume simulations: Cosmological constraints from sky survey populations
Evrard, A. E.
MacFarland, T. J.
Couchman, H. M. P.
Colberg, J. M.
Yoshida, N.
White, S. D. M.
Jenkins, A.
Frenk, C. S.
Pearce, F. R.
Peacock, J. A.
Thomas, P. A.
cosmology : theory; dark matter; galaxies : clusters : general; intergalactic medium
We use gigaparticle N-body simulations to study galaxy cluster populations in Hubble volumes of LambdaCDM (Omega(m) = 0.3, Omega(Lambda) = 0.7) and tauCDM (Omega(m) = 1) world models. Mapping past light cones of locations in the computational space, we create mock sky surveys of dark matter structure to z similar or equal to 1.4 over 10,000 deg(2) and to z similar or equal to 0.5 over two full spheres. Calibrating the Jenkins mass function at z = 0 with samples of 1.5 million clusters, we show that the fit describes the sky survey counts to less than or similar to20% accuracy over all redshifts for systems more massive than poor galaxy groups (5 x 10(13) h(-1) M.). Fitting the observed local temperature function determines the ratio beta of specific thermal energies in dark matter and intracluster gas. We derive a scaling with power spectrum normalization beta proportional to sigma(8)(5/3) and find that the LambdaCDM model requires sigma(8) = 1.04 to match beta = 1.17 derived from gasdynamic cluster simulations. We estimate a 10% overall systematic uncertainty in sigma(8), 4% arising from cosmic variance in the local sample and the bulk from uncertainty in the absolute mass scale of clusters. Considering distant clusters, the LambdaCDM model matches Extended Medium- Sensitivity Survey and ROSAT Deep Cluster Survey X-ray selected observations under economical assumptions for intracluster gas evolution. Using transformations of mass-limited cluster samples that mimic sigma(8) variation, we explore Sunyaev- Zeldovich (SZ) search expectations for a 10 deg(2) survey complete above 10(14) h(-1) M.. Cluster counts are shown to be extremely sensitive to sigma(8) uncertainty, while redshift statistics, such as the sample median, are much more stable. Redshift information is crucial to extract the full cosmological diagnostic power of SZ cluster surveys. For LambdaCDM, the characteristic temperature at a fixed sky surface density is a weak function of redshift, implying an abundance of hot clusters at z > 1. Assuming constant beta, one 8 keV cluster at z > 2 and 10 5 keV clusters at z > 3 are expected in the Sloan Digital Sky Survey area. Too many such clusters can falsify the model; detection of clusters more massive than Coma at z > 1 violates LambdaCDM at 95% confidence if their surface density exceeds 0.003 deg(-2), or 120 on the whole sky.
2002
Article
http://edoc.mpg.de/12138
urn:ISSN:0004-637X
The Astrophysical Journal, v.573, 7-36 (2002)
en
oai:edoc.mpg.de:121502006-10-1625:114
Isotropic Raman line shapes near gas-liquid critical points: The shift, width, and asymmetry of coupled and uncoupled states of fluid nitrogen
Musso, M.
Matthai, F.
Keutel, D.
Oehme, K. L.
In order to improve the experimental database about the additional nonrotational broadening of vibrational line shapes observable when a simple fluid approaches its gas-liquid critical point, we improved the pioneering measurements of Clouter and Kiefte [for their own review see Phys. Rev. A 33, 2749 (1986)] on the critical behavior of the polarized Raman line of fluid nitrogen by using the isotopic mixture (N- 14(2))(.975)-((NN)-N-14-N-15)(.025), giving special attention to the fact that the isotropic line shape of liquid N-2 ((ν) over tilde approximate to2327 cm(-1)) is affected by intermolecular vibrational resonance couplings. Using a highest-resolution double monochromator and modern CCD detection techniques, we were able to follow the temperature dependencies of the line shape parameters (i.e., shift, width, and asymmetry) of the coupled N-14(2) and, depending on the S/N ratio available, of the uncoupled (NN)-N-14-N-15 in the range 45 Kless than or similar toTless than or similar to300 K with up to mK resolution (1) in the beta-solid phase, (2) in the coexisting liquid and gas phases, and (3) along the critical isochore. Comparing the line shifts of both isotopic species, clear evidence was found that vibrational resonance couplings are present in all dense phases studied, the line position (ν) over tilde (0) being more density than temperature dependent. Additionally, the existence of (negative) cross correlations between resonant and nonresonant dephasing mechanisms has been confirmed by the change in sign observed for the small but non-negligible difference in the linewidths between coupled N-14(2) and uncoupled (NN)-N-14-N-15 around 90 K. The lambda-shaped dependencies of the width parameters, observed when moving along the coexistence line through the critical point, T-crit=126.192 K, and along the critical isochore, is much more evident in the line asymmetry than in the usually considered linewidth. Clear proof was found that, in accordance with theoretical predictions, the linewidth converges to a constant maximum value regardless if the critical point is reached along the coexistence line or along the critical isochore, i.e., it does not diverge approaching the critical temperature up to our closest value \T/T-crit- 1\approximate to10(-5). (C) 2002 American Institute of Physics.
2002
Article
http://edoc.mpg.de/12150
urn:ISSN:0021-9606
Journal of Chemical Physics, v.116, 8015-8027 (2002)
en
oai:edoc.mpg.de:121542006-10-1625:114
Lensing by Lyman-limit systems: Determining the mass-to-gas ratio
Maller, A. H.
Kolatt, T. S.
Bartelmann, M.
Blumenthal, G. R.
dark matter; galaxies : formation; gravitational lensing; quasars : absorption lines
We present a new method for determining the total mass-to- neutral gas ratio Y (H) (I) in Lyman-limit absorption systems. The method exploits the relation between the neutral hydrogen column density and the magnification of background sources due to weak gravitational lensing by these systems. Since weak lensing does not measure the mass directly, this relation must be inverted in a statistical sense to solve for the average (sic)(H) (I) and its distribution. We demonstrate the feasibility of this approach by using a detailed mock catalog of quasars (sources) and Lyman-limit systems ( lenses) and by showing our ability to recover the parameter (sic)(H) (I). This mock catalog also allows us to check for systematics in the method and to sketch its limitations. For a universal constant (sic)(H) (I) and a sample of n(QSO) quasars, we obtain an unbiased estimate of (sic)(H) (I) with 95% confidence levels of +/-140 (10(5)/n(QSO))(1/2), where the error bars are independent of (sic)(H) (I).
2002
Article
http://edoc.mpg.de/12154
urn:ISSN:0004-637X
The Astrophysical Journal, v.569, 72-82 (2002)
en
oai:edoc.mpg.de:121582011-02-1425:114
The first detection of weak gravitational shear in infrared observations: Abell 1689
King, L. J.
Clowe, D. I.
Lidman, C.
Schneider, P.
Erben, T.
Kneib, J. P.
Meylan, G.
2002
Article
http://edoc.mpg.de/12158
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.385, L5-L9 (2002)
en
oai:edoc.mpg.de:121602006-10-1625:114
Modelling the IGM and the Ly alpha forest at high redshift from the dark matter distribution
Viel, M.
Matarrese, S.
Mo, H. J.
Theuns, T.
Haehnelt, M. G.
intergalactic medium; quasars : absorption lines; cosmology : theory; large-scale structure of Universe
A variety of approximate schemes for modelling the low-density intergalactic medium (IGM) in the high-redshift Universe are compared with the results of a large high-resolution hydrodynamical simulation. These schemes use either an analytical description of the dark matter distribution and the IGM or numerical simulations of the dark matter (DM) distributions combined with different approximate relations between dark matter field and the gas distribution. Schemes based on a filtering of the dark matter distribution with a global Jeans scale result in a rather poor description of the gas distribution. An adaptive filtering which takes into account the density/temperature dependence of the Jeans scale is required. A reasonable description of the gas distribution can be achieved using a fit of the mean relation between the dark matter and gas densities in the hydrodynamical simulation to relate dark matter and gas distribution. In the hydrodynamical simulations deviations from this mean relation are correlated with gradients in the dark matter peculiar velocity field indicative of shocks in the gas component. A scheme which takes into account this correlation results in a further improved gas distribution. Such adaptive filtering schemes applied to dark matter simulations will be very well suited for studies of statistical properties of the Lyalpha forest which investigate the IGM and the underlying dark matter distribution and require a large dynamic range and/or an extensive parameter study.
2002
Article
http://edoc.mpg.de/12160
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.336, 685-698 (2002)
en
oai:edoc.mpg.de:121672006-10-1625:114
Galaxy formation in pre-heated intergalactic media
Mo, H. J.
Mao, S.
galaxies : clusters : general; galaxies : elliptical and lenticular; cD; galaxies : formation; galaxies : spiral; galaxies : structure
We outline a scenario of galaxy formation in which the gas in galaxy-forming regions was pre-heated to high entropy by vigorous energy feedback associated with the formation of stars in old ellipticals and bulges and with active galactic nuclei activity. Such pre-heating probably occurred at redshifts of z similar to2-3, and can produce the entropy excess observed today in low-mass clusters of galaxies without destroying the bulk of the Lyalpha forest. Subsequent galaxy formation is affected by the pre-heating, because the gas no longer follows the dark matter on galaxy scales. The hot gas around galaxy haloes has very shallow profiles and emits only weakly in the X-ray range. Cooling in a pre-heated halo is not inside-out, because the cooling efficiency does not change significantly with radius. Only part of the gas in a protogalaxy region can cool and be accreted into the final galaxy halo by the present time. The accreted gas is probably in diffuse clouds and so does not lose angular momentum to the dark matter. Cluster ellipticals are produced by mergers of stellar systems formed prior to the pre-heating, while large galaxy discs form in low- density environments where gas accretion can continue to the present time.
2002
Article
http://edoc.mpg.de/12167
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.333, 768-778 (2002)
en
oai:edoc.mpg.de:121712006-10-1625:114
Parameterised models for the lensing cluster Abell 1689
King, L. J.
Clowe, D. I.
Schneider, P.
dark matter; gravitational lensing; large-scale structure of Universe; galaxies : clusters : general; methods : statistical
Here we apply a recently developed maximum likelihood method for determining best-fit parameterised lens models to observations of the rich lensing cluster Abell 1689. The observations that we use were taken with the ESO/MPG Wide Field Imager. The wide field-of-view enables us to use the weakly lensed images of faint background objects on an unsurpassed range of scales, 0.12 h(-1) Mpc < R<1.8 h(-1) Mpc from the cluster centre, to determine best-fit models for the 1- parameter singular isothermal sphere (SIS), 2-parameter general power-law and NFW models, and 3-parameter singular isothermal ellipsoid (SIE). The best-fit SIS has an Einstein radius theta(E) = 0'.37 (0.043 h(-1) Mpc) i.e. a velocity dispersion sigma(1D) = 1028(-42)(+35) km s(-1) in an Omega = 1.0, Lambda = 0.0 cosmology. For the best-fit NFW profile, the virial radius r(200) = 1.14 h(-1) Mpc and the concentration parameter c = 4.7, giving a virial mass M-200 = 5.7 x 10(14) h(-1) M-circle dot. At q = 0.88, the slope of the best-fit power-law model is slightly flatter than isothermal (q = 1:0), indicating that the galaxies most important in the fitting procedure lie inside the scale radius r(s). By fitting an SIE, the deviation of the projected mass distribution from circular symmetry is evident, with a best-fit axial ratio f=0.74.
2002
Article
http://edoc.mpg.de/12171
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.383, 118-124 (2002)
en
oai:edoc.mpg.de:121792006-10-1625:114
B-modes in cosmic shear from source redshift clustering
Schneider, P.
van Waerbeke, L.
Mellier, Y.
cosmology; gravitational lensing; large-scale structure of the Universe
Weak gravitational lensing by the large scale structure can be used to probe the dark matter distribution in the Universe directly and thus to probe cosmological models. The recent detection of cosmic shear by several groups has demonstrated the feasibility of this new mode of observational cosmology. In the currently most extensive analysis of cosmic shear, it was found that the shear field contains unexpected modes, so-called B-modes, which are thought to be unaccountable for by lensing. B-modes can in principle be generated by an intrinsic alignment of galaxies from which the shear is measured, or may signify some remaining systematics in the data reduction and analysis. In this paper we show that B-modes in fact are produced by lensing itself. The effect comes about through the clustering of source galaxies, which in particular implies an angular separation-dependent clustering in redshift. After presenting the theory of the decomposition of a general shear field into E- and B-modes, we calculate their respective power spectra and correlation functions for a clustered source distribution. Numerical and analytical estimates of the relative strength of these two modes show that the resulting B-mode is very small on angular scales larger than a few arcminutes, but its relative contribution rises quickly towards smaller angular scales, with comparable power in both modes at a few arcseconds. The relevance of this effect with regard to the current cosmic shear surveys is discussed; it can not account for the apparent detection of a B-mode contribution on large angular scales in the cosmic shear analysis of van Waerbeke et al. (2002).
2002
Article
http://edoc.mpg.de/12179
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.389, 729-741 (2002)
en
oai:edoc.mpg.de:121892006-10-1625:114
The MACHO project Large Magellanic Cloud variable star inventory. XII. Three Cepheid variables in eclipsing binaries
Alcock, C.
Allsman, R. A.
Alves, D. R.
Becker, A. C.
Bennett, D. P.
Cook, K. H.
Drake, A. J.
Freeman, K. C.
Griest, K.
Hawley, S. L.
Keller, S.
Lehner, M. J.
Lepischak, D.
Marshall, S. L.
Minniti, D.
Nelson, C. A.
Peterson, B. A.
Popowski, P.
Pratt, M. R.
Quinn, P. J.
Rodgers, A. W.
Suntzeff, N.
Sutherland, W.
Vandehei, T.
Welch, D. L.
binaries : eclipsing; Cepheids; Magellanic Clouds; stars : AGB and post-AGB; stars : oscillations
We present a method for solving the light curve of an eclipsing binary system that contains a Cepheid variable as one of its components as well as the solutions for three eclipsing Cepheids in the Large Magellanic Cloud (LMC). A geometric model is constructed in which the component stars are assumed to be spherical and on circular orbits. The emergent system flux is computed as a function of time, with the intrinsic variations in temperature and radius of the Cepheid treated self- consistently. Fitting the adopted model to photometric observations, incorporating data from multiple bandpasses, yields a single parameter set best describing the system. This method is applied to three eclipsing Cepheid systems from the MACHO project LMC database: MACHO 6.6454.5, 78.6338.24, and 81.8997.87. A best-fit value is obtained for each systems orbital period and inclination and for the relative radius, color, and limb-darkening coefficients of each star. Pulsation periods and parameterizations of the intrinsic color variations of the Cepheids are also obtained, and the amplitude of the radial pulsation of each Cepheid is measured directly. The system 6.6454.5 is found to contain a 4.97 day Cepheid, which cannot be definitely classified as type I or type II, with an unexpectedly brighter companion. The system 78.6338.24 consists of a 17.7 day, W Virginis class type II Cepheid with a smaller, dimmer companion. The system 81.8997.87 contains an intermediate-mass, 2.03 day overtone Cepheid with a dimmer, red giant secondary.
2002
Article
http://edoc.mpg.de/12189
urn:ISSN:0004-637X
The Astrophysical Journal, v.573, 338-350 (2002)
en
oai:edoc.mpg.de:121932006-10-1625:114
The nature of the ultraluminous X-ray Sources inside galaxies and their relation to local QSOs
Burbidge, G.
Burbidge, E. M.
Arp, H.
2003
Article
http://edoc.mpg.de/12193
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.400, L17-L19 (2003)
en
oai:edoc.mpg.de:126062006-10-1625:114
Kosmologie
Börner, Gerhard
S.Fischer
2002 S.Fischer
2002
Book
http://edoc.mpg.de/12606
urn:ISBN:3-596-15355-7
Fischer Kompakt, v.15355 (2002)
de
oai:edoc.mpg.de:128442006-10-1625:114
The influence of radiative effects on the accretion onto stellar magnetospheres
Kryukov, I. A.
Pogorelov, N. V.
Anzer, U.
Bisnovatyi-Kogan, G. S.
Börner, G.
2003
Article
http://edoc.mpg.de/12844
urn:ISSN:0004-6361
Astronomy & Astrophysics, v.402, 13-28 (2003)
en
oai:edoc.mpg.de:128892006-10-1625:114
Gamma Rays from Intergalactic Shocks
Keshet, Uri
Waxman, Eli
Loeb, Abraham
Springel, Volker
Hernquist, Lars
2003
Article
http://edoc.mpg.de/12889
urn:ISSN:0004-6361
The Astrophysical Journal, v.585, 128-150 (2003)
en
oai:edoc.mpg.de:128962006-10-1625:114
Selection of Metal-poor Giant Stars Using the Sloan Digital Sky Survey Photometric System
Helmi, Amina
Ivezic, Zeljko
Prada, Francisco
Pentericci, Laura
Rockosi, Constance M.
Schneider, Donald P.
Grebel, Eva K.
Harbeck, Daniel
Lupton, Robert H.
Gunn, James E.
Knapp, Gillian R.
Strauss, Michael A.
Brinkmann, Jonathan
2003
Article
http://edoc.mpg.de/12896
urn:ISSN:0004-637X
The Astrophysical Journal, v.586, 195-200 (2003)
en
oai:edoc.mpg.de:129632011-03-1725:114
Error estimates for measurements of cosmic shear
Munshi, Dipak
Coles, Peter
2003
Article
http://edoc.mpg.de/12963
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.338, 846-856 (2003)
en
oai:edoc.mpg.de:133752006-10-1625:114
Constraining galaxy formation and cosmology with the conditional luminosity function of galaxies
Yang, Xiaohu
Mo, H. J.
van den Bosch, Frank C.
2003
Article
http://edoc.mpg.de/13375
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.399, 1057-1080 (2003)
en
oai:edoc.mpg.de:133762011-02-1125:114
COBE-DMR constraints on the non-linear coupling parameter: a wavelet based method
Cayón, L.
Martínez-González, E.
Argüeso, F.
Banday, A. J.
Górski, K. M.
2003
Article
http://edoc.mpg.de/13376
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.339, 1189-1194 (2003)
en
oai:edoc.mpg.de:133772006-10-1625:114
Predictions for statistical properties of forming spheroidal galaxies
Perrotta, F.
Magliocchetti, M.
Baccigalupi, C.
Bartelmann, M.
De Zotti, G.
Granato, G. L.
Silva, L.
Danese, L.
gravitational lensing; galaxies : formation; large-scale structure of Universe; submillimetre
We show that the features of the recent astrophysically motivated model by Granato et al. are fully consistent with the available statistical measurements of galaxies at (sub)millimetre wavelengths. We quantitatively predict the impact of this scenario on near-future cosmological observations dealing with spatial and flux statistical distribution of (sub)millimetre galaxies. We show that the expected angular correlation function of spheroids is compatible with available data. We compute the expected power spectrum of fluctuations due to clustering at the frequencies of the High Frequency Instrument (HFI) on ESA's Planck satellite: the clustering signal is found to be detectable in regions of low interstellar dust emission. A further distinctive prediction of the adopted model is a remarkably high fraction of gravitationally lensed sources at bright millimetre/submillimetre fluxes. In fact, since most spheroids bum at redshift z similar or equal to 2-3 according to the adopted model, gravitational lensing amplifies a significant number of high-z forming spheroidal galaxies, which will be detectable by large-area, shallow surveys at millimetre/submillimetre wavelengths, such as those carried out by Planck/HFI. Allowing for other source populations, we find that the fraction of gravitationally lensed millimetre/submillimetre sources at fluxes > 100 mJy is expected to be up to similar or equal to40 per cent.
2003
Article
http://edoc.mpg.de/13377
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.338, 623-636 (2003)
en
oai:edoc.mpg.de:133782006-10-1625:114
Cluster cross-sections for strong lensing: analytic and numerical lens models
Meneghetti, Massimo
Bartelmann, Matthias
Moscardini, Lauro
2003
Article
http://edoc.mpg.de/13378
urn:ISSN:0035-8711
Monthly Notices of the Royal Astronomical Society, v.340, 105-114 (2003)
en
oai:edoc.mpg.de:134792006-10-1625:114
Fast, exact CMB power spectrum estimation for a certain class of observational strategies
Wandelt, B. D.
Hansen, F. K.
We describe a class of observational strategies for probing the anisotropies in the cosmic microwave background (CMB) where the instrument scans on rings which can be combined into an n- torus, the ring torus. This class has the remarkable property that it allows an exact maximum likelihood power spectrum estimation in operations of order N-2 (if the size of the data set is N) under circumstances which would previously have made this analysis intractable: correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes, nonuniform distribution of integration time on the sky, and partial sky coverage. This ease of computation gives us an important theoretical tool for understanding the impact of instrumental effects on CMB observables and hence for the design and analysis of CMB observations in the future. There are members of this class which closely approximate the MAP and Planck satellite missions. We present a numerical example where we apply our ring torus methods to a simulated data set from a CMB mission covering a 20degrees patch on the sky to compute the maximum likelihood estimate of the power spectrum C-l with unprecedented efficiency.
2003
Article
http://edoc.mpg.de/13479
urn:ISSN:0556-2821
Physical Review D, v.67, 023001-1-023001-9 (2003)
en
oai:edoc.mpg.de:134882006-10-1625:114
The influence of clumping on surface brightness fits of edge-on spiral galaxies
Misiriotis, A.
Bianchi, S.
radiative transfer; ISM : dust; extinction; galaxies : photometry; galaxies : spiral; galaxies : structure
We have used a Monte Carlo radiative transfer code to produce edge-on images of dusty galactic disks, allowing a fraction of the dust to be distributed in clumps. Synthetic images of edge- on galaxies have been constructed for different amounts of dust, distributions of clumps and fractions of dust in clumps, following the formalism of Bianchi et al. (2000a). We have also considered models with stellar emission embedded in the clumps. The synthetic images have been fitted with analytical models made with smooth distributions of dust, adopting the procedure developed by Xilouris et al. (1999) to fit optical images of real edge-on galaxies. We have compared the parameters determined by the fit with the input parameters of the models. For the clumping distributions adopted in this paper, the neglect of clumping results in underestimating the amount of dust in a galaxy. However, the underestimation is never larger than 40%.
2002
Article
http://edoc.mpg.de/13488
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.384, 866-871 (2002)
en
oai:edoc.mpg.de:134892006-10-1625:114
Der polarisierte Hintergrund
Bartelmann, Matthias
2003
Article
http://edoc.mpg.de/13489
urn:ISSN:0039-1263
Sterne und Weltraum, v.42, 26-28 (2003)
de
oai:edoc.mpg.de:134902006-10-1625:114
ESO Imaging Survey - Exploring the optical/infrared imaging data of CDF-S: Point sources
Hatziminaoglou, E.
Groenewegen, M. A. T.
da Costa, L.
Arnouts, S.
Benoist, C.
Madejsky, R.
Mignani, R. P.
Olsen, L. F.
Rite, C.
Schirmer, M.
Slijkhuis, R.
Vandame, B.
surveys; quasars; stars : white dwarves; stars : low mass; brown dwarves
This paper describes the methodology currently being implemented in the EIS pipeline for analysing optical/infrared multi-colour data. The aim is to identify different classes of objects as well as possible undesirable features associated with the construction of colour catalogues. The classification method used is based on the chi(2)-fitting of template spectra to the observed SEDs, as measured through broad-band filters. Its main advantage is the simultaneous use of all colours, properly weighted by the photometric errors. In addition, it provides basic information on the properties of the classified objects (e.g. redshift, effective temperature). These characteristics make the chi(2)-technique ideal for handling large multi-band datasets. The results are compared to the more traditional colour-colour selection and, whenever possible, to model predictions. In order to identify objects with odd colours, either associated with rare populations or to possible problems in the catalogue, outliers are searched for in the multi-dimensional colour space using a nearest-neighbour criterion. Outliers with large chi(2)-values are individually inspected to further investigate their nature. The tools developed are used for a preliminary analysis of the multi- colour point source catalogue constructed from the optical/infrared imaging data obtained for the Chandra Deep Field South (CDF-S). These data are publicly available, representing the first installment of the ongoing EIS Deep Public Survey.
2002
Article
http://edoc.mpg.de/13490
urn:ISSN:1432-0746
Astronomy & Astrophysics, v.384, 81-98 (2002)
en
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