X-ray properties of dust-obscured galaxies with broad optical/UV emission lines

TL;DR

This study examines the X-ray properties of dust-obscured galaxies with broad optical/UV emission lines, revealing their high accretion rates, moderate obscuration, and implications for galaxy and black hole co-evolution.

Contribution

It presents the first X-ray analysis of DOGs with broad emission lines, highlighting their high Eddington ratios and role in galaxy-black hole growth.

Findings

High Eddington ratios in DOGs suggest active black hole growth.

DOGs exhibit moderate X-ray luminosities with significant obscuration.

Relations among X-ray, infrared, and bolometric luminosities are consistent with expectations.

Abstract

Dust-obscured galaxies (DOGs) with extreme infrared luminosities may represent a key phase in the co-evolution of galaxies and supermassive black holes. We select 12 DOGs at $0.3\lesssim z\lesssim1.0$ with broad Mg II or H$\beta$ emission lines and investigate their X-ray properties utilizing snapshot observations ($\sim3~\mathrm{ks}$ per source) with Chandra. By assuming that the broad lines are broadened due to virial motions of broad-line regions, we find that our sources generally have high Eddington ratios ($\lambda_\mathrm{Edd}$). Our sources generally have moderate intrinsic X-ray luminosities ($L_\mathrm{X}\lesssim10^{45}~\mathrm{erg~s^{-1}}$), which are similar to those of other DOGs, but are more obscured. They also present moderate outflows and intense starbursts. Based on these findings, we conclude that high-$\lambda_\mathrm{Edd}$ DOGs are closer to the peaks of both host-galaxy and black-hole growth compared to other DOGs, and that AGN feedback has not swept away their reservoirs of gas. However, we cannot fully rule out the possibility that the broad lines are broadened by outflows, at least for some sources. We investigate the relations among $L_\mathrm{X}$, AGN rest-frame $6~\mathrm{\mu m}$ monochromatic luminosity, and AGN bolometric luminosity, and find the relations are consistent with the expected ones.