Galaxy Formation with Local Photoionization Feedback -II. Effect of
  X-Ray Emission from Binaries and Hot Gas
  We study how X-rays from stellar binary systems and the hot intracluster
medium (ICM) affect the radiative cooling rates of gas in galaxies. Our study
uses a novel implementation of gas cooling in the moving-mesh hydrodynamics
code \textsc{arepo}. X-rays from stellar binaries do not affect cooling at all
as their emission spectrum is too hard to effectively couple with galactic gas.
In contrast, X-rays from the ICM couple well with gas in the temperature range
$10^4 - 10^6$ K. Idealised simulations show that the hot halo radiation field
has minimal impact on the dynamics of cooling flows in clusters because of the
high virial temperature ($> 10^7$K), making the interaction between the gas and
incident photons very ineffective. Satellite galaxies in cluster environments,
on the other hand, experience a high radiation flux due to the emission from
the host halo. Low mass satellites ($< 10^{12}\rm{M_\odot}$) in particular have
virial temperatures that are exactly in the regime where the effect of the
radiation field is maximal. Idealised simulations of satellite galaxies
including only the effect of host halo radiation (no ram pressure stripping or
tidal effects) fields show a drastic reduction in the amount of cool gas formed
($\sim 40\%$) on a short timescale of about $0.5$ Gyrs. A galaxy merger
simulation including all the other environmental quenching mechanisms, shows
about $20\%$ reduction in the stellar mass of the satellite and about $\sim
30\%$ reduction in star formation rate after $1$ Gyr due to the host hot halo
radiation field. These results indicate that the hot halo radiation fields
potentially play an important role in quenching galaxies in cluster
environments.
