Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of
  Galaxy Clusters
  Astro-H will be the first X-ray observatory to employ a high-resolution
microcalorimeter, capable of measuring the shift and width of individual
spectral lines to the precision necessary for estimating the velocity of the
diffuse plasma in galaxy clusters. This new capability is expected to bring
significant progress in understanding the dynamics, and therefore the physics,
of the intracluster medium. However, because this plasma is optically thin,
projection effects will be an important complicating factor in interpreting
future Astro-H measurements. To study these effects in detail, we performed an
analysis of the velocity field from simulations of a galaxy cluster
experiencing gas sloshing, and generated synthetic X-ray spectra, convolved
with model Astro-H Soft X-ray Spectrometer (SXS) responses. We find that the
sloshing motions produce velocity signatures that will be observable by Astro-H
in nearby clusters: the shifting of the line centroid produced by the
fast-moving cold gas underneath the front surface, and line broadening produced
by the smooth variation of this motion along the line of sight. The line shapes
arising from inviscid or strongly viscous simulations are very similar,
indicating that placing constraints on the gas viscosity from these
measurements will be difficult. Our spectroscopic analysis demonstrates that,
for adequate exposures, Astro-H will be able to recover the first two moments
of the velocity distribution of these motions accurately, and in some cases
multiple velocity components may be discerned. The simulations also confirm the
importance of accurate treatment of PSF scattering in the interpretation of
Astro-H/SXS spectra of cluster plasmas.
