A Rapidly Accreting Active Galactic Nucleus Hidden in a Dust-obscured Galaxy at z ∼ 0.8

Dust-obscured galaxies (DOGs) containing central supermassive black holes (SMBHs) that are rapidly accreting (i.e., having high Eddington ratios, lambda( Edd)) may represent a key phase closest to the peak of both the black hole and galaxy growth in the coevolution framework for SMBHs and galaxies. In this work, we present a 68 ks XMM-Newton observation of the high-lambda( Edd) DOG J1324+4501 at z similar to 0.8, which was initially observed by Chandra. We analyze the XMM-Newton spectra jointly with archival Chandra spectra. In performing a detailed X-ray spectral analysis, we find that the source is intrinsically X-ray luminous with log(L-X /erg s(-1))=44.71(-0.12)(+0.08) and heavily obscured with log(N-H/cm(-2))=23.43(-0.13)(+0.09) . We further utilize UV-to-IR archival photometry to measure and fit the source's spectral energy distribution to estimate its host-galaxy properties. We present a supplementary comparison sample of 21 X-ray luminous DOGs from the XMM-SERVS survey with sufficient (>200) 0.5-10 keV counts to perform a similarly detailed X-ray spectral analysis. Of the X-ray luminous DOGs in our sample, we find that J1324+4501 is the most remarkable, possessing one of the highest X-ray luminosities, column densities, and star formation rates. We demonstrate that J1324+4501 is in an extreme evolutionary stage where SMBH accretion and galaxy growth are at their peaks.