A Rapidly Accreting Active Galactic Nucleus Hidden in a Dust-Obscured Galaxy at $z\sim 0.8$

Abstract

Dust-obscured galaxies (DOGs) containing central supermassive black holes (SMBHs) that are rapidly accreting (i.e., having high Eddington ratios, $\hat{I}{»}_{\mathrm{Edd}}$) 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-$\hat{I}{»}_{\mathrm{Edd}}$ DOG J1324+4501 at \mbox{$z\sim 0.8$}, which was initially observed by Chandra. We analyze the XMM-Newton spectra jointly with archival Chandra spectra. In performing a detailed \mbox{X-ray} spectral analysis, we find that the source is intrinsically \mbox{X-ray} luminous with $\log (L_{\mathrm{X}}$/erg s${}^{-1})=44.71_{-0.12}^{+0.08}$ and heavily obscured with $\log (N_{\mathrm{H}}/{\mathrm{cm}}^{-2})=23.43_{-0.13}^{+0.09}$. We further utilize UV-to-IR archival photometry to measure and fit the source's spectral energy distribution (SED) to estimate its host-galaxy properties. We present a supplementary comparison sample of 21 \mbox{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 \mbox{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.

13 pages, 6 figures, 3 tables, accepted for publication in ApJ