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Astro-H will be the first X-ray observatory to employ a high-resolutionmicrocalorimeter, capable of measuring the shift and width of individualspectral lines to the precision necessary for estimating the velocity of thediffuse plasma in galaxy clusters. This new capability is expected to bringsignificant 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 interpretingfuture Astro-H measurements. To study these effects in detail, we performed ananalysis of the velocity field from simulations of a galaxy clusterexperiencing gas sloshing, and generated synthetic X-ray spectra, convolvedwith model Astro-H Soft X-ray Spectrometer (SXS) responses. We find that thesloshing motions produce velocity signatures that will be observable by Astro-Hin nearby clusters: the shifting of the line centroid produced by thefast-moving cold gas underneath the front surface, and line broadening producedby the smooth variation of this motion along the line of sight. The line shapesarising from inviscid or strongly viscous simulations are very similar,indicating that placing constraints on the gas viscosity from thesemeasurements will be difficult. Our spectroscopic analysis demonstrates that,for adequate exposures, Astro-H will be able to recover the first two momentsof the velocity distribution of these motions accurately, and in some casesmultiple velocity components may be discerned. The simulations also confirm theimportance of accurate treatment of PSF scattering in the interpretation ofAstro-H/SXS spectra of cluster plasmas.

Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of Galaxy Clusters