A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2
Arjun Dey, B. T. Soifer, Vandana Desai, Kate Brand, Emeric LeFloc'h, Michael J. Brown, Buell T. Jannuzi, Lee Armus, Shane Bussmann, Mark Brodwin, Chao Bian, Pet… 展开作者
Arjun Dey, B. T. Soifer, Vandana Desai, Kate Brand, Emeric LeFloc'h, Michael J. Brown, Buell T. Jannuzi, Lee Armus, Shane Bussmann, Mark Brodwin, Chao Bian, Peter Eisenhardt, Sarah Higdon, Daniel Weedman, Steve Willner
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Accepted for publication in the Astrophysical Journal
Observations with Spitzer Space Telescope have recently revealed a significant population of high-redshift z~2 dust-obscured galaxies (DOGs) with large mid-IR to UV luminosity ratios. These galaxies have been missed in traditional optical studies of the distant universe. We present a simple method for selecting this high-z population based solely on the ratio of the observed mid-IR 24um to optical R-band flux density. In the 8.6 sq.deg Bootes NDWFS Field, we uncover ~2,600 DOG candidates (= 0.089/sq.arcmin) with 24um flux densities F24>0.3mJy and (R-[24])>14 (i.e., F[24]/F[R] > 1000). These galaxies have no counterparts in the local universe, and become a larger fraction of the population at fainter F24, representing 13% of the sources at 0.3~mJy. DOGs exhibit evidence of both star-formation and AGN activity, with the brighter 24um sources being more AGN- dominated. We have measured spectroscopic redshifts for 86 DOGs, and find a broad z distribution centered at <z>~2.0. Their space density is 2.82E-5 per cubic Mpc, similar to that of bright sub-mm-selected galaxies at z~2. These redshifts imply very large luminosities LIR>~1E12-14 Lsun. DOGs contribute ~45-100% of the IR luminosity density contributed by all z~2 ULIRGs, suggesting that our simple selection criterion identifies the bulk of z~2 ULIRGs. DOGs may be the progenitors of ~4L* present-day galaxies seen undergoing a luminous,short- lived phase of bulge and black hole growth. They may represent a brief evolution phase between SMGs and less obscured quasars or galaxies. [Abridged]
