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

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]$\lambda 5008$ 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 $N_{\mathrm{H}}=10^{23-24}\mathrm{c}{\mathrm{m}}^{-2}$. We identify 20 X-ray-non-detected ERQs at high mid-infrared luminosities of $\nu L_{\nu ,6\mu \mathrm{m}}\gtrsim 3\times 10^{46}\mathrm{erg}{\mathrm{s}}^{-1}$. By stacking the X-ray observations, we find that the non-detected ERQs are on average underluminous in X-rays by a factor of $\sim 10$ 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.

24 pages, 10 figures, Accepted to ApJ

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