Gas Accretion, Galactic Winds and the Circumgalactic Medium in Cosmological Galaxy Formation Simulations

How gas is accreted onto galactic halos from the intergalactic medium (IGM), processed in galaxies and ejected back to the environment are crucial questions in understanding galaxy formation and evolution. Studies of the spacial distribution, chemical composition, kinematics and ionization states of the gas within several hundreds kpc -- the circumgalactic medium (CGM) -- provide clues to understanding this cycle of baryons. In this talk, I will present a detailed study of the co-evolution of the galaxy-CGM ecosystem using two suites of cosmological, hydrodynamic simulations with mass ranging from Milky Way analogs to dwarf galaxies. The simulations adopt a blastwave scheme for supernova feedback which naturally produces large-scale galactic outflows, metal-dependent radiative cooling, and a model for the turbulent mixing of heavy elements. The simulations successfully reproduce many observational properties, including mass budget in different components and various galactic structural properties. I will discuss the origins of the enriched CGM around massive galaxies at high redshift, and identify the relative contributions from the central galaxy and its accreting satellites. I will then present a detailed comparison with the absorption line studies on the distribution, kinematics and evolution of neutral hydrogen (H I) and commonly-observed metal ions (Si II, Si IV, C II, C IV and O VI) in the CGM. We find that the CGM exhibits highly multi-phase structures with kinematically aligned high and low-ionization metal absorbers. The absorption strength as a function of the the impact parameter is in good agreement with observations for all ions. The cold accretion flows probed by Lyman-limit systems (LLSs) can be enriched substantially from dwarf satellites and re-accreted outflows, making them detectable using low ionization metal species (such as MgII).  If time permits, I will also discuss how these observed CGM properties depend on stellar feedback, radiative cooling and the mixing of metals.