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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 198575.0, MPI für Astronomie / Publikationen_mpia
Starburst in HS 0822+3542 induced by the very blue LSB dwarf SAO 0822+3545
Authors:Pustilnik, S. A.; Kniazev, A. Y.; Pramskij, A. G.; Ugryumov, A. V.; Masegosa, J.
Date of Publication (YYYY-MM-DD):2003
Title of Journal:Astronomy and Astrophysics
Journal Abbrev.:Astronomy and Astrophysics
Start Page:917
End Page:932
Review Status:not specified
Audience:Not Specified
Abstract / Description:One of the most metal-deficient blue compact
galaxies (BCGs) HS 0822+3542 (Z=1/34
Zsun), is also one of the nearest such
objects (D ~ 11 Mpc). It is in addition well
isolated from known bright galaxies. A trigger
mechanism for its current star-formation (SF)
burst has thus remained unclear. We report the
discovery of a very blue ((B-V)0_tot=
0.08 and (V-R)0_tot= 0.14) low
surface brightness (LSB) (mu
B0 gtrsim 23\fm4
arcsec-2) dwarf irregular (dIrr)
galaxy, which we have named SAO 0822+3545. Its
small relative velocity and projected distance of
only ~ 11 kpc from the BCG imply their physical
association. For this LSB dIrr galaxy, we
present spectroscopic results, total B,V,R
magnitudes, and the effective radii and surface
brightness (SB), and we describe its morphological
properties. We compare the very blue colours of
this dwarf with PEGASE.2 models of the colour
evolution of a Z=1/20 Zsun stellar
population, and combine this analysis with the
data on the LSBD EW(H alpha; ) values. The
models best describing all available
observational data depend on the relative
fraction of massive stars in the IMF used. For a
Salpeter IMF with M_up = 120 Msun,
the best model includes a ``young'' single
stellar population (SSP) with an age of ~ 10
Myr and an ``old'' SSP with the age of ~ 0.2-10
Gyr. The mass ratio of the old to young
components should be in the range of 10 to 30.
If the age of the old component is more than ~
1 Gyr, an additional coeval component of
``intermediate'' age ( ~ 100 Myr) with a mass
comparable to that of the ``young'' population,
although not required, provided a good fit to the
current data. For the two options of a model IMF
biased toward the low-mass end, the best match
of the observed BVR and EW(H alpha; ) is for
continuous star-formation rate (SFR)
single-component models, with SF durations in
the range of ~ 0.1 to ~ 1 Gyr. However, only a
longer time-scale SF gives the stellar mass,
compatible with the LSB galaxy mass estimates.
Nevertheless, such a scenario would be
inconsistent with the recent encounter of these
two dwarfs. The role of interaction between the
LSBD and BCG HS 0822+3542 in triggering their
major SF episodes during the last ~ 100-200 Myr
is emphasized and discussed. For the BCG, based
on the results of new spectroscopy with the
Russian 6 m telescope, we estimate the physical
parameters of its SF region and present the first
evidence of an ionized gas supershell. This pair
of dwarfs lies deep within the nearby
Lynx-Cancer void, with the nearest bright (L
gt; L*) galaxies at distances
gt;3 Mpc. This is probably one of the main
factors responsible for the unevolved state of HS
Free Keywords:galaxies: interactions; galaxies: photometry;
; galaxies: abundances; galaxies: individual: HS
; 0822+3542; SAO 0822+3545
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
External Affiliations:Nizhnij Arkhyz, Karachai-Circassia 369167,
Russia; Isaac Newton Institute of Chile, SAO
Branch), AB(Special Astrophysical Observatory
RAS, Nizhnij Arkhyz, Karachai-Circassia 369167,
Russia; Max Planck Institut f uuml;r Astronomie,
K ouml;nigstuhl 17, 69117 Heidelberg, Germany;
Isaac Newton Institute of Chile, SAO Branch),
AC(Special Astrophysical Observatory RAS, Nizhnij
Arkhyz, Karachai-Circassia 369167, Russia; Isaac
Newton Institute of Chile, SAO Branch),
AD(Special Astrophysical Observatory RAS, Nizhnij
Arkhyz, Karachai-Circassia 369167, Russia; Isaac
Newton Institute of Chile, SAO Branch),
AE(Instituto de Astrofisica de Andaluc iacute;a,
Granada, Spain)
Identifiers:URL:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bi... [ID No:1]
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