Evidence for Intrinsic X-ray Weakness Among Red Quasars at Cosmic Noon

TL;DR

This study reveals that extremely red quasars at cosmic noon are heavily obscured and intrinsically X-ray weak, with the X-ray weakness linked to stronger outflows, suggesting a connection between accretion processes and feedback mechanisms.

Contribution

It provides the first comprehensive X-ray analysis of 50 ERQs, demonstrating their intrinsic X-ray weakness and its correlation with high-velocity outflows, advancing understanding of quasar feedback.

Findings

ERQs are heavily obscured with high gas column densities.

X-ray non-detected ERQs are underluminous by a factor of ~10.

X-ray weakness correlates with higher-velocity outflows.

Abstract

Quasar feedback is a key ingredient in shaping galaxy evolution. A rare population of extremely red quasars (ERQs) at $z=2-3$ are often associated with high-velocity [O III]$\lambda5008$ outflows and may represent sites of strong feedback. In this paper, we present an X-ray study of 50 ERQs to investigate the link between the X-ray and outflow properties of these intriguing objects. Using hardness ratio analysis, we confirm that the ERQs are heavily obscured systems with gas column density reaching $N_\mathrm{H}=10^{23-24}\,\mathrm{cm^{-2}}$. We identify 20 X-ray-non-detected ERQs at high mid-infrared luminosities of $\nu L_\mathrm{\nu,6\mu m}\gtrsim3\times10^{46}\,\mathrm{erg\,s^{-1}}$. By stacking the X-ray observations, we find that the non-detected ERQs are on average underluminous in X-rays by a factor of $\sim10$ for their mid-infrared luminosities. We consider such X-ray weakness to be due to both heavy gas absorption and intrinsic factors. Moreover, we find that the X-ray-weak sources also display higher-velocity outflows. One option to explain this trend is that weaker X-rays facilitate more vigorous line-driven winds, which then accelerate the \oiii-emitting gas to kpc-scales. Alternatively, super-Eddington accretion could also lead to intrinsic X-ray weakness and more powerful continuum-driven outflow.