Gas Kinematics in a Galaxy’s Circumgalacitc Medium (CGM): Simulation and Observation

The circumgalactic medium (CGM) surrounding a galaxy may provide additional fuel to sustain the galaxy’s star formation rate through gas accretion. However, this has been under debate since neither the current observed HI accretion rate is sufficient nor direct evidence of ionized gas accretion is presented. To address both issues, first I will show that the gas mass of the Milky Way’s CGM has been underestimated by nearly 50% in spectroscopic observations which favor high velocity gas to avoid Galactic emission/absorption. This is done by performing synthetic observations of the CGM of a simulated MW-mass galaxy, in which we mimic the inside-out observational patterns of local observers and incorporate galactic differential rotation in understanding the CGM’s kinematics. Second, from observational perspective I will present direct evidence of ionized gas accretion at the disk-halo interface of M33 using new HST-COS observations of a set of O type stars in the disk of M33. I will also present a suite of warm/warm-hot gas accretion models and discuss how the observed accreting phenomena fit into these scenarios. By combining this UV dataset with HI data from GALFA-HI, I seek to obtain an insight into the multiphase gas structures at the disk-halo interface and to clarify the role of gas accretion in sustain a galaxy’s star forming activities.