Hot Dust-Obscured Galaxies with Excess Blue Light

Hot Dust-Obscured Galaxies (Hot DOGs) are among the most luminous galaxies in the Universe. Powered by highly obscured, possibly Compton-thick, active galactic nuclei (AGNs), Hot DOGs are characterized by SEDs that are very red in the mid-IR yet dominated by the host galaxy stellar emission in the UV and optical. An earlier study identified a sub-sample of Hot DOGs with significantly enhanced UV emission. One target, W0204–0506, was studied in detail and, based on Chandra observations, it was concluded that the enhanced emission was most likely due to either extreme unobscured star-formation (SFR > 1000 M⊙ yr−1) or to light from the highly obscured AGN scattered by gas or dust into our line of sight. Here, we present a follow-up study of W0204–0506 as well as two more Hot DOGs with excess UV emission. For the two new objects we obtained Chandra/ACIS-S observations, and for all three targets we obtained HST/WFC3 F555W and F160W imaging. The analysis of these observations, combined with multi-wavelength photometry and UV/optical spectroscopy suggest that UV emission is most likely dominated by light from the central highly obscured, hyper-luminous AGN that has been scattered into our line of sight, by either gas or dust. We cannot decisively rule out, however, that star-formation or a second AGN in the system may significantly contribute to the UV excess of these targets.