Half of the Most Luminous Quasars May Be Obscured: Investigating the Nature of WISE-Selected Hot Dust-Obscured Galaxies

Creators: Assef, R. J.; Einsenhardt, P. R. M.; Stern, D.; Tsai, C.-W.; Wu, J.; Wylezalek, D.; Blain, A. W.; Bridge, C. R.; Donoso, E.; Gonzales, A.; Griffith, R. L.; Jarrett, T. H.

Abstract

The Wide-field Infrared Survey Explorer mission has unveiled a rare population of high-redshift (z = 1–4.6), dusty, hyper-luminous galaxies, with infrared luminosities L_(IR) > 10^(13)L_☉, and sometimes exceeding 10^(14)L_☉. Previous work has shown that their dust temperatures and overall far-infrared spectral energy distributions (SEDs) are significantly hotter than expected to be powered by star formation. We present here an analysis of the rest-frame optical through mid-infrared SEDs for a large sample of these so-called "hot, dust-obscured galaxies" (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured active galactic nuclei (AGNs) that dominates the rest-frame emission at λ > 1 µm and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as 10^(11)–10^(12) M_⊙, the AGN emission, with a range of luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit, at a level at least 10 times more efficiently than z ~ 2 QSOs. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This may be at odds with the trend suggested at lower luminosities for the fraction of obscured AGNs to decrease with increasing luminosity. That trend may, instead, reverse at higher luminosities. Alternatively, Hot DOGs may not be the torus-obscured counterparts of the known optically selected, largely unobscured, hyper-luminous QSOs, and may represent a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and statistically show that these objects are in regions as dense as those of known high-redshift proto-clusters.

Additional Information

© 2015 American Astronomical Society. Received 2014 August 4; accepted 2015 February 19; published 2015 April 27. We are indebted to all WISE team members. We thank the anonymous referee for comments and suggestions that helped to improve this article. RJA was supported by Gemini-CONICYT grant number 32120009. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Kitt Peak National Observatory and CTIO, National Optical Astronomy Observatory, are operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory. The SOAR Telescope is a joint project of: Conselho Nacional de Pesquisas Científicas e Tecnológicas CNPq-Brazil, The University of North Carolina at Chapel Hill, Michigan State University, and the National Optical Astronomy Observatory. Based partly on observations obtained at the Hale Telescope, Palomar Observatory as part of a continuing collaboration between the California Institute of Technology, NASA/JPL, NOAO, Oxford University, Stony Brook University, and the National Astronomical Observatories of China. This material is based upon work supported by the National Aeronautics and Space Administration under Proposal No. 13-ADAP13-0092 issued through the Astrophysics Data Analysis Program. Facilities: WISE, Spitzer (IRAC), Hale (WIRC), MMT (SWIRC), SOAR (OSIRIS), WIYN (WHIRC).

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