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, which are least affected by non-gravitational gas physics, as well as to measurements probing gas properties in filamentary structures.