Abstract
Hydrodynamic simulations of galaxies that include stellar feedback are now
able to comfortably reproduce observations of the cool halo gas around
star-forming galaxies. Without implementing quasar feedback, however, these
simulations under-predict the cool gas content of quasar host halos by more
than a factor of two. To better understand the source of this tension, we have
compiled an exhaustive sample of 195 quasars at z=1 with constraints on
chemically enriched, cool gas traced by MgII absorption in background quasar
spectra from the Sloan Digital Sky Survey. We find a strong correlation between
quasar luminosity and cool gas covering fraction. In particular, low-luminosity
quasars exhibit a mean gas covering fraction comparable to inactive galaxies of
similar masses, but more luminous quasars exhibit excess cool gas approaching
what is reported previously at z=2.2. Moreover, 40% of the MgII absorption
occurs at radial velocities of |v|>300 km/s from the quasar systemic redshift,
inconsistent with gas gravitationally bound to the quasar host halo. We discuss
possible scenarios to explain the large velocity offsets and observed
luminosity dependence of the cool gas near quasars including gas arising in:
(1) neighboring halos correlated through large-scale structure at Mpc scales,
(2) feedback from luminous quasars, and (3) debris from the mergers thought to
trigger luminous quasars. The first of these scenarios can be ruled out by the
lack of correlation between quasar luminosity and clustering while the latter
two each make distinct predictions that can be tested with additional
observations.
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