Virialization of Gas in Dark Matter Halos and its Implications for Galaxy Evolution

Gas in dark matter halos, known as the circumgalactic medium (CGM), is both the source of fuel for star formation in the galaxy and the destination of galaxy outflows. The CGM is thus expected to play a fundamental role in galaxy evolution. I will revisit the question of the virialization of the CGM, in which the volume-filling gas phase transitions from being predominantly cool and free-falling at low halo masses to predominantly hot and quasi-static at high halo masses. Using both an idealized model and the FIRE cosmological simulations, I will demonstrate that several aspects of this process have not been previously appreciated despite over four decades of research. I will then show that CGM virialization in FIRE is associated with an abrupt change in the properties of star formation and outflows in the central galaxy, and with the formation of a galaxy disc.