The fight between cooling and heating in clusters of galaxies

Clusters of galaxies are the largest gravitationally-bound individual objects in the Universe. The vast majority of their baryonic mass is found in the form of hot 10^6-8 K gas, known as the intracluster medium (ICM). The density of this gas strongly increases in the cores of the galaxies where the radiative cooling time is less than 1 Gyr. Theoretical models predict large mass deposition of up to 100s of solar masses per year in the cores of these objects. Such high values are not detected, in particular there is a significant lack of cool gas below 6 · 10^6 K, presumably due to heating produced by galaxy mergers, sloshing of gas within the gravitational field or most likely by the tremendous amount of energy that is thrown by matter accreting on the supermassive (10^6-9 Msun) black holes host in the centers of the galaxies. It is still under debate which of these scenarios is most feasible, but possibly each of them is relevant at certain galactic or cluster scales. I will provide a summary of the current state of art and show some recent discoveries that shed new light on the processes responsible for the balance between gas heating and cooling in clusters of galaxies. Particular focus is given on advanced techniques in high-resolution X-ray spectroscopy, which will be crucial with the launch of the new X-ray mission ASTRO-H and the preparation of the ATHENA X-ray satellite, the new frontier of X-ray astronomy.

Speaker: Ciro Pinto, University of Cambridge