High redshift extremely red quasars in X-rays
  Quasars may have played a key role in limiting the stellar mass of massive
galaxies. Identifying those quasars in the process of removing star formation
fuel from their hosts is an exciting ongoing challenge in extragalactic
astronomy. In this paper we present X-ray observations of eleven extremely red
quasars (ERQs) with $L_{\rm bol}\sim 10^{47}$ erg s$^{-1}$ at $z=1.5-3.2$ with
evidence for high-velocity ($v > 1000$ km s$^{-1}$) [OIII]$\lambda$5007\AA\
outflows. X-rays allow us to directly probe circumnuclear obscuration and to
measure the instantaneous accretion luminosity. We detect ten out of eleven
extremely red quasars available in targeted and archival data. Using a
combination of X-ray spectral fitting and hardness ratios, we find that all of
the ERQs show signs of absorption in the X-rays with inferred column densities
of $N_{\rm H}\approx 10^{23}$ cm$^{-2}$, including four Compton-thick
candidates ($N_{\rm H} > 10^{24}$ cm$^{-2}$). We stack the X-ray emission of
the seven weakly detected sources, measuring an average column density of
$N_{\rm H}\sim 8\times 10^{23}$ cm$^{-2}$. The absorption-corrected (intrinsic)
$2-10$ keV X-ray luminosity of the stack is $2.7\times 10^{45}$ erg s$^{-1}$,
consistent with X-ray luminosities of type 1 quasars of the same infrared
luminosity. Thus, we find that ERQs are a highly obscured, borderline
Compton-thick population, and based on optical and infrared data we suggest
that these objects are partially hidden by their own equatorial outflows.
However, unlike some quasars with known outflows, ERQs do not appear to be
intrinsically underluminous in X-rays for their bolometric luminosity. Our
observations indicate that low X-rays are not necessary to enable some types of
radiatively driven winds.
