Hot Baryons in Deep Potential Wells: IXO Studies of Hot Gas in Galaxies, Groups and Clusters

Clusters of galaxies are the largest collapsed, virialized systems in the Universe with total masses up to 10¹⁵ M_⊙. While most of the mass in clusters is dark matter, most of the baryonic mass is in the form of a hot (T=10^7-8 K), optically thin plasma that is only visible through its X-ray emission. Clusters of galaxies represent one of the few places in the Universe where the intergalactic medium "lights up" and is bright enough to study in detail. The X-rays emitted by the hot, diffuse gas provide a unique view of not only the structure of clusters and the distribution of dark matter in the cluster potential wells, but also of how gravity and other physical processes act on matter to create the galaxies.

IXO studies are crucially important for understanding the physics of clusters, including the interactions between galaxies and the ICM. The growth of clusters through mergers, and the distribution of metals. Through the measurement of line broadening, line shifts, and the distribution of the heavy elements in the cluster gas, IXO opens a new window on the physical processes occurring in cluster gas: turbulence, bulk motions, enrichment, and magnetic fields. IXO's high spectral resolution and large throughput will allow us to measure bulk motions and turbulence an order of magnitude better than previous observatories including XMM, Astro-H and SRG, for the first time at or even below the levels expected from simulations of structure formation.