Astronomy Colloquium

The circumgalactic medium (CGM; non-ISM gas within a galaxy virial radius) regulates the gas flows that shape the assembly and evolution of galaxies. It most likely contains enough material to harbor most of the metals lost in galaxy winds and to sustain star-formation for billions of years.  Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of HST/COS, observations and simulations of the CGM have emerged as the new frontier of galaxy evolution studies. In this talk, I will describe observational constraints we have placed on the origin and fate of this material by studying the gas kinematics, metallicity and ionization state of gas 10 - 200 kpc from galaxies' stars. I will conclude by introducing several exciting new techniques for resolving the gaseous structures in the CGM, and by posing unanswered questions about the CGM that will be addressed with future survey data and hydrodynamic simulations in a cosmological context.