THE NATURE OF FAINT SPITZER-SELECTED DUST-OBSCURED GALAXIES

We use deep far-IR, submillimeter, radio, and X-ray imaging and mid-IR spectroscopy to explore the nature of a sample of Spitzer-selected dust-obscured galaxies (DOGs) in GOODS-N. A sample of 79 galaxies satisfy the criteria R - [24] - 14 ( Vega) down to S(24) > 100 mu Jy (median flux density S(24) 180 mu Jy). Twelve of these galaxies have IRS spectra available, which we use to measure redshifts and classify these objects as being dominated by star formation or active galactic nucleus (AGN) activity in the mid- IR. The IRS spectra and Spitzer photometric redshifts confirm that the DOGs lie in a tight redshift distribution around z similar to 2. Based on mid- IR colors, 80% of DOGs are likely dominated by star formation; the stacked X- ray emission fromthis subsample of DOGs is also consistent with star formation. Since only a small number of DOGs are individually detected at far- IR and submillimeter wavelengths, we use a stacking analysis to determine the average flux from these objects and plot a composite IR (8-1000 mu m) spectral energy distribution (SED). The average luminosity of these star- forming DOGs is L(IR) similar to 1 x 10(12) L(circle dot). We compare the average star-formingDOGto the average bright (S(850) > 5 mJy) submillimeter galaxy (SMG); the S(24) > 100 mu Jy DOGs are 3 times more numerous but 8 times less luminous in the IR. The far-IR SED shape of DOGs is similar to that of SMGs (average dust temperature of around 30 K), but DOGs have a higher mid- IR-to-far-IR flux ratio. The average star formationYdominatedDOG has a star formation rate of 200 M(circle dot) yr(-1), which, given their space density, amounts to a contribution of 0.01 M(circle dot) yr(-1) Mpc(-3) ( or 5% -10%) to the star formation rate density at z similar to 2.