<b>ASTRONOMY COLLOQUIUM</b><br>Why the Invisible Reservoir of Gas Around Galaxies Counts in Galaxy Evolution
<i>Note: Distinguished Alumnus Colloquium</i>
Galaxies like the Milky Way are engaged in an evolving balancing act among gas supply, consumption, and removal. Many of the baryons involved in this cycle are in a phase that is difficult to observe directly--diffuse, highly-ionized gas in the halo, aka the circumgalactic medium. In this talk I will present absorption-line observations of the CGM that help to reveal the physical and dynamical state of circumgalactic gas. I will show that under simple assumptions such as ionization equilibrium, the cool and warm phases of the CGM (T < 10^6 K) can account for most of the baryons purported to be missing from dark matter halos of both star-forming and passive galaxies with M_halo ~ 10^12. Yet, under these same assumptions, the cool (10^4 K) gas in the CGM is far from pressure equilibrium with a hot medium (10^6 K) that could provide hydrostatic support. I will present new (and future) survey data that will not only address several outstanding questions related to the CGM but will ultimately enable a more complete picture of both the CGM and the cosmic web surrounding it.
Jessica Werk (University of Washington)