Exploring the hot/cold gas in the centers of galaxy clusters

Shutaro Ueda  (ASIAA)

Galaxy clusters contain a large amount of hot, diffuse X-ray emitting gas known as the intracluster medium (ICM; T ~ 10^7-8 Kelvin), which is thermalized within the gravitational potential well dominated by dark matter. Cool cores are often located at the centers of galaxy clusters, and are in the form of the dense, relatively cool, metal enriched ICM. The presence of cool cores poses a challenge for our understanding of the thermal evolution of the ICM, which is known as the cooling flow problem in cluster astrophysics, based on the fact that X-ray observations have indicated no evidence of cooling flows. However, recent ALMA observations have found a substantial amount of molecular gas especially CO-gas (10^7-10 Msun) in the centers of galaxy clusters. In this talk, I will introduce a hypothesis of the cooling flow and recent my works on the cooling flow problem. Additionally, I will present a new project for exploring cold atomic gas in the cluster center with ALMA.