Cooling, heating and gas evolution in the circumgalactic medium

Abstract

The Universe at large scales consists of gravitationally bound dark matter halos. Ordinary gas inside the halos emits and also absorbs the radiation from background sources leaving distinct signatures for multi-wavelength observations. Broadly, the gas is in three primary dynamical states: firstly, in-falling into the potential well of the halo; secondly, remains within the halo in (quasi)hydrostatic equilibrium until it radiatively cools; thirdly, gets ejected from the halo by strong out flows driven by a central black hole or stars. The gas within the halos and outside the central galaxy (hosting the black hole and stars) is called the circumgalactic medium (CGM), and specifically, intracluster medium (ICM) in the most massive halos (& 1014 M ). In this thesis, I will discuss the thermodynamic and dynamical state of the diffuse ICM/CGM. Observations indicate that the ICM does not cool as efficiently as predicted in the theory including pure radiative cooling. Radio, X-ray and H observations now suggest that the central black hole is injecting a copious amount of energy in clusters to maintain a global thermal balance. Using results from my numerical simulations, I will discuss how locally thermally unstable ICM becomes multiphase (temperature ranges: 104 ð€€€107 K). One of the useful tracers to detect multiphase gas in clusters is the ratio of cooling time to the free-fall time (tcool=t ) measured for hot gas. I will mention the constraints imposed on this tracer under a wide range of physical conditions. I will further discuss how the entropy pro les of the hot gas gets reset by cooling/feedback and may modify the nature of multiphase condensation. Lastly, I will discuss about the cooling, heating and gas evolution in the CGMs of smaller halos. I will conclude my thesis with a summary and future directions.