Testing X-ray Measurements of Galaxy Cluster Outskirts with Cosmological
  Simulations
  The study of galaxy cluster outskirts has emerged as one of the new frontiers
in extragalactic astrophysics and cosmology with the advent of new observations
in X-ray and microwave. However, the thermodynamic properties and chemical
enrichment of this diffuse and azimuthally asymmetric component of the
intracluster medium (ICM) are still not well understood. This work, for the
first time, systematically explores potential observational biases in these
regions. To assess X-ray measurements of galaxy cluster properties at large
radii ($>{R}_{500c}$), we use mock Chandra analyses of cosmological galaxy
cluster simulations. The pipeline is identical to that used for Chandra
observations, but the biases discussed in this paper are relevant for all X-ray
observations outside of ${R}_{500c}$. We find the following from our analysis:
(1) filament regions can contribute as much as $50\%$ at $R_{200c}$ to the
emission measure; (2) X-ray temperatures and metal abundances from model fitted
mock X-ray spectra in a multi-temperature ICM respectively vary to the level of
$10\%$ and $50\%$; (3) resulting density profiles vary to within $10\%$ out to
$R_{200c}$, and gas mass, total mass, and baryon fractions all vary to within a
few percent; (4) the bias from a metal abundance extrapolated a factor of five
higher than the true metal abundance results in total mass measurements biased
high by $20\%$ and total gas measurements biased low by $10\%$; and (5)
differences in projection and dynamical state of a cluster can lead to gas
density slope measurements that differ by a factor of $15\%$ and $30\%$,
respectively. The presented results can partially account for some of the
recent gas profile measurements in cluster outskirts by, e.g., Suzaku. Our
findings are pertinent to future X-ray cosmological constraints from cluster
outskirts.
