The X-ray Link Between High Eddington Ratio Dust-Obscured Galaxies (DOGs) and Hot DOGs

TL;DR

This study investigates the X-ray properties of high Eddington ratio dust-obscured galaxies, revealing they are heavily obscured and likely represent a post-merger phase with enshrouded AGNs, similar to Hot DOGs.

Contribution

It provides new X-ray observational evidence linking high Eddington ratio DOGs to Hot DOGs, suggesting a common evolutionary stage in galaxy growth.

Findings

Most high-Eddington DOGs are heavily obscured with high column densities.

High-Eddington DOGs share properties with Hot DOGs, indicating a similar evolutionary phase.

These galaxies are likely in a post-merger stage with enshrouded AGNs.

Abstract

Dust-obscured galaxies (DOGs) with extremely red optical-to-infrared colors are often associated with intense starburst and AGN activity. Studying DOGs can provide insights into the processes that drive the growth of galaxies and their central supermassive black holes. However, the general DOG population is heterogeneous, spanning a wide range of evolutionary stages, and has X-ray obscuring column densities ($N_\mathrm{H}$) covering low-to-high levels. In this work, we focus on seven high Eddington ratio DOGs ($\log \lambda_\mathrm{Edd} \gtrsim -0.5$) to examine their X-ray obscuration properties using new and archival X-ray observations. We confirm that these systems are generally heavily obscured, with 6/7 having $N_\mathrm{H}\gtrsim10^{23}~\mathrm{cm^{-2}}$ and 3/7 having $N_\mathrm{H}\gtrsim10^{24}~\mathrm{cm^{-2}}$. Based on the observed similarity with the rare Hot DOG population, we argue that both high-$\lambda_\mathrm{Edd}$ DOGs and Hot DOGs likely trace the post-merger phase during which AGNs are enshrouded by large columns of dust-rich material.