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          Institute: MPI für extraterrestrische Physik     Collection: High Energy Astrophysics at MPE     Display Documents

ID: 12612.0, MPI für extraterrestrische Physik / High Energy Astrophysics at MPE
Optical and radio properties of extragalactic sources observed by the first survey and the Sloan Digital Sky Survey
Authors:Ivezic, Zeljko; Menou, Kristen; Knapp, Gillian R.; Strauss, Michael A.; Lupton, Robert H.; Vanden Berk, Daniel E.; Richards, Gordon T.; Tremonti, Christy; Weinstein, Michael A.; Anderson, Scott; Bahcall, Neta A.; Becker, Robert H.; Bernardi, Mariangela; Blanton, Michael; Eisenstein, Daniel; Fan, Xiaohui; Finkbeiner, Douglas; Finlator, Kristian; Frieman, Joshua; Gunn, James E.; Hall, Pat B.; Kim, Rita S. J.; Kinkhabwala, Ali; Narayanan, Vijay K.; Rockosi, Constance M.; Schlegel, David; Schneider, Donald P.; Strateva, Iskra; SubbaRao, Mark; Thakar, Aniruddha R.; Voges, Wolfgang; White, Rrichard L.; Yanny, Brian; Brinkmann, Jonathan; Doi, Mamoru; Fukugita, Masataka; Hennessy, Gregory S.; Munn, Jeffrey A.; Nichol, Robert C.; York, Donald G.
Date of Publication (YYYY-MM-DD):2002-11
Title of Journal:The Astronomical Journal
Journal Abbrev.:Astron. J.
Issue / Number:5
Start Page:2364
End Page:2400
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We discuss the optical and radio properties of similar to30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 1."5 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r*similar to22.2) source in 1230 deg(2) of sky. The matched sample represents similar to30% of the 108,000 FIRST sources and 0.1% of the 2.5x10(7) SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20, 000 quasars in 1030 deg(2) of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r*=21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from similar to50% at the bright end to similar to90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of similar to5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux optical flux plane suggests the existence of the "quasar radio dichotomy" 8%+/-1% of all quasars with i*<18.5 are radio-loud, and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08&PLUSMN;0.02 mag, and show a 3 times larger fraction of objects with extremely red colors. FIRST galaxies represent 5% of all SDSS galaxies with r*<17.5, and 1% for r*<20, and are dominated by red (u*-r*>2.22) galaxies, especially those with r*>17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN(30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r*<17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.
Free Keywords:galaxies : active; galaxies : photometry; quasars : general; radio continuum
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für extraterrestrische Physik
External Affiliations:Princeton Univ Observ, Peyton Hall, Princeton, NJ 08544 USA; Princeton Univ Observ, Princeton, NJ 08544 USA; Fermilab Natl Accelerator Lab, Batavia, IL 60510 USA; Penn State Univ, Dept Astron & Astrophys, Davey Lab 525, University Pk, PA 16802 USA; Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA; Univ Washington, Dept Astron, Seattle, WA 98195 USA; Univ Calif Davis, Dept Phys, Davis, CA 95616 USA; Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 USA; NYU, Dept Phys, New York, NY 10003 USA; Univ Arizona, Steward Observ, Tucson, AZ 85721 USA; Inst Adv Study, Princeton, NJ 08540 USA; Pontificia Univ Catolica Chile, Fac Fis, Dept Astron & Astrofis, Santiago 22, Chile; Max Planck Inst Extraterr Phys, D-85741 Garching, Germany; Space Telescope Sci Inst, Baltimore, MD 21218 USA; Apache Point Observ, Sunspot, NM 88349 USA; Univ Tokyo, Inst Astron, Tokyo 1810015, Japan; Univ Tokyo, Res Ctr Early Universe, Tokyo 1810015, Japan; Univ Tokyo, Inst Cosm Ray Res, Kashiwa, Chiba 2778582, Japan; USN Observ, Washington, DC 20392 USA; USN Observ, Flagstaff Stn, Flagstaff, AZ 86002 USA; Carnegie Mellon Univ, Dept Phys, Pittsburgh, PA 15232 USA
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