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Title:
A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2
Authors:
Dey, Arjun; Soifer, B. T.; Desai, Vandana; Brand, Kate; Le Floc'h, Emeric; Brown, Michael J. I.; Jannuzi, Buell T.; Armus, Lee; Bussmann, Shane; Brodwin, Mark; Bian, Chao; Eisenhardt, Peter; Higdon, Sarah J.; Weedman, Daniel; Willner, S. P.
Affiliation:
AA(National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719; .), AB(Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125.; Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125.), AC(Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125.), AD(Space Telescope Science Institute, Baltimore, MD 21218; Giacconi Fellow.), AE(Institute for Astronomy, University of Hawaii, Honolulu, HI 96822.; Spitzer Fellow.), AF(School of Physics, Monash University, Clayton, Victoria 3800, Australia.), AG(National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719; .), AH(Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125.), AI(Steward Observatory, University of Arizona, Tucson, AZ 85721.), AJ(National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719; .), AK(Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125.), AL(Jet Propulsion Laboratory, California Institute of Technology, MC 169-327, 4800 Oak Grove Drive, Pasadena, CA 91109.), AM(Georgia Southern University, P. O. Box 8031, Statesboro, GA.), AN(Astronomy Department, Cornell University, Ithaca, NY 14853.), AO(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.)
Publication:
The Astrophysical Journal, Volume 677, Issue 2, pp. 943-956. (ApJ Homepage)
Publication Date:
04/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Formation, Galaxies: High-Redshift, Galaxies: Starburst
Abstract Copyright:
(c) 2008: The American Astronomical Society
DOI:
10.1086/529516
Bibliographic Code:
2008ApJ...677..943D

Abstract

The Spitzer Space Telescope has revealed a significant population of high-redshift (z~2) dust-obscured galaxies with large mid-infrared to ultraviolet luminosity ratios. Due to their optical faintness, these galaxies have been previously missed in traditional optical studies of the distant universe. We present a simple method for selecting this high-redshift population based solely on the ratio of the observed mid-infrared 24 μm to optical R-band flux density. We apply this method to observations of the ~8.6 deg2 NOAO Deep Wide-Field Survey Boötes field, and uncover ~2600 dust-obscured galaxy candidates [i.e., 0.089 arcmin-2) with 24 μm flux densities F24μm>=0.3 mJy and (R-[24])>=14 (i.e., Fν(24μm)/Fν(R)>~1000]. These galaxies have no counterparts in the local universe. They represent 7%+/-0.6% of the 24 μm source population at F24μm>=1 mJy but increase to ~13%+/-1% of the population at ~0.3 mJy. These galaxies exhibit evidence of both star formation and AGN activity, with the brighter 24 μm sources being more AGN-dominated. We have measured spectroscopic redshifts for 86 of these galaxies, and find a broad redshift distribution centered at z¯~1.99+/-0.05. The space density of this population is ΣDOG(F24μm>=0.3 mJy)=(2.82+/-0.05)×10-5h370 Mpc-3, similar to that of bright submillimeter-selected galaxies at comparable redshifts. These redshifts imply large luminosities, with median νLν(8 μm)~4×1011 Lsolar. The infrared luminosity density contributed by this relatively rare dust-obscured galaxy population is log(IRLD)~8.23+0.18-0.30. This is ~60+40-15% of that contributed by z~2 ultraluminous infrared galaxies (ULIRGs, with LIR>1012 Lsolar) our simple selection thus identifies a significant fraction of z~2 ULIRGs. This IRLD is ~26%+/-14% of the total contributed by all z~2 galaxies. We suggest that these dust-obscured galaxies are the progenitors of luminous (~4L*) present-day galaxies, seen undergoing an extremely luminous, short-lived phase of both bulge and black hole growth. They may represent a brief evolutionary phase between submillimeter-selected galaxies and less obscured quasars or galaxies.
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