Galaxy cluster cosmology and astrophysics with XRISM

When the XRISM X-ray observatory begins operations later this year, it will provide an unprecedented combination of high spectral resolution, large collecting area, and broad-band X-ray coverage, enabling new insights into many areas of astrophysics. The capability to precisely measure line-of-sight motion in spatially resolved regions promises to transform the study of galaxy clusters, allowing direct measurements of ICM bulk motions and turbulent velocity within and away from the cluster core. These measurements in turn will place interesting constraints on the non-thermal pressure support in relaxed clusters, with implications for cosmologically important X-ray mass estimates. We present the capabilities of XRISM and describe the initial observing campaign designed to perform these measurements, which will serve as a benchmark for future XRISM observations to expand the sample of clusters with direct ICM velocity measurements. We also discuss the cluster astrophysics that can be addressed by XRISM, which among other things will help us to understand the role of AGN feedback in shaping the dynamics, chemical composition, and thermal state of the atmospheric plasma near the cluster core, and to validate atomic models for which XRISM will provide unique data currently unavailable by other means.