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The Astrophysical Journal Volume 679 Number 2 Create an alert RSS this journal

Vandana Desai et al. 2008 ApJ 679 1204 doi:10.1086/587637

Redshift Distribution of Extragalactic 24 μm Sources* **

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Vandana Desai1,2, B. T. Soifer1,2, Arjun Dey3, Buell T. Jannuzi3, Emeric Le Floc'h4,5,6, Chao Bian1, Kate Brand3,7, Michael J. I. Brown8, Lee Armus2, Dan W. Weedman9, Richard Cool5, Daniel Stern10 and Mark Brodwin3

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Abstract References Cited By
We present the redshift distribution of a complete, unbiased sample of 24 μm sources down to fν(24 μ m) = 300 μ Jy (5 σ). The sample consists of 591 sources detected in the Boötes field of the NOAO Deep Wide-Field Survey. We have obtained optical spectroscopic redshifts for 421 sources (71%). These have a redshift distribution peaking at z ~ 0.3, with a possible additional peak at z ~ 0.9, and objects detected out to z = 4.5. The spectra of the remaining 170 (29%) exhibit no strong emission lines from which to determine a redshift. We develop an algorithm to estimate the redshift distribution of these sources, based on the assumption that they have emission lines but that these lines are not observable due to the limited wavelength coverage of our spectroscopic observations. The redshift distribution derived from all 591 sources exhibits an additional peak of extremely luminous (L8–1000 μ m > 3 × 1012 Lsun) objects at z ~ 2, consisting primarily of sources without observable emission lines. We use optical line diagnostics and IRAC colors to estimate that 55% of the sources within this peak are AGN-dominated. We compare our results to published models of the evolution of infrared-luminous galaxies. The models which best reproduce our observations predict a large population of star-formation-dominated ULIRGs at z > 1.5 rather than the AGN-dominated sources we observe.

Footnote
*  Based on observations made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory under NASA contract 1407.
Footnote
**  Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Subject headings

galaxies: distances and redshifts; galaxies: evolution; galaxies: formation; infrared: galaxies


Dates

Issue 2 (2008 June 1)

Received 2007 September 9, accepted for publication 2008 February 18



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