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

TL;DR

This study uses simulated Astro-H observations to analyze gas sloshing motions in galaxy cluster cores, demonstrating the observability of velocity signatures and the importance of accounting for projection effects and instrument response.

Contribution

The paper presents the first detailed simulation-based analysis of Astro-H's capability to detect and interpret gas motions in galaxy clusters, considering projection effects and instrument response.

Findings

Gas sloshing motions produce observable velocity signatures.

Astro-H can recover velocity distribution moments accurately.

PSF scattering significantly affects spectral interpretation.

Abstract

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.