A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2

April 2008 • 2008ApJ...677..943D

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.

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 F_{24 μ m} >= 0.3 mJy and (R - [ 24]) >= 14 (i.e., F_ν(24 μ m)/F_ν(R) gtrsim 1000]. These galaxies have no counterparts in the local universe. They represent 7% +/- 0.6% of the 24 μm source population at F_{24 μ m} >= 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 \overline{z}≈ 1.99+/- 0.05. The space density of this population is Σ_DOG(F_{24μ m} >= 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 ν L_ν(8 μ m) ≈ 4 × 10¹¹ L_⊙. 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 L_IR > 10¹² L_⊙) 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.

Links

• PREPRINT http://arxiv.org/abs/0801.1860
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2008ApJ...677..943D
• ELECTR https://doi.org/10.1086%2F529516
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2008ApJ...677..943D
• PDF https://stacks.iop.org/0004-637X/677/943/pdf
• DATA https://archive.gemini.edu/searchform/publication=2008ApJ...677..943D
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2008ApJ...677..943D
• DATA https://irsa.ipac.caltech.edu/bibdata/2008/D/2008ApJ...677..943D.html