Author(s): S.H. Ho, C.L. Martin, Physics, University of California, Santa Barbara, Santa Barbara, California, UNITED STATES|G.G. Kacprzak, Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, AUSTRALIA|C.W. Churchill, New Mexico State University, Las Cruces, New Mexico, UNITED STATES|M.L. Turner, Las Cumbres Observatory, Goleta, California, UNITED STATES|
Institution(s): 1. Physics, University of California, Santa Barbara, Santa Barbara, CA, United States. 2. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC, Australia. 3. New Mexico State University, Las Cruces, NM, United States. 4. Las Cumbres Observatory, Goleta, CA, United States.
Contributing team(s): (none)
Galactic disks grow by accreting cooling gas from the circumgalactic medium (CGM). Decades of observations have also demonstrated that galaxies need a continuous gas supply to explain the star formation history and the stellar metallicity distribution of disks. However, direct observations of gas accretion onto galaxies remain sparse. I will present results of our survey that measures the kinematics of low-ionization-state gas in the CGM. We have observed quasars behind star-forming galaxies at z=0.2, and the quasar sightlines pass within 100 kpc of the foreground galaxies. We find that the Doppler shift of the circumgalactic absorption shares the same sign as the quasar side of the galactic disk, but the Doppler shifts are smaller than disk rotation predicts. The Doppler sign correlation implies the low-ionization-state gas in the inner CGM corotates with the disk. Altogether, our results indicate centrifugal force partially supports the circumgalactic gas, and therefore the angular momentum of the CGM delays accretion onto the disk. We have modeled the absorption kinematics using an inflow model with gas spiraling inwards near the disk plane. The model predicts the 3D orientation of the disk, which we test with new measurements. Our results suggest galaxies typically have inflow speeds of around 40 km/s, comparable to that of the cold inflowing gas we have identified around galaxies in the EAGLE simulations. We also find cold rotating gas disks with inflowing gas in EAGLE, and these disks extend to radii comparable to the impact parameters of our quasar sightlines around galaxies. Our analysis with EAGLE thereby further supports our inflow interpretation for the circumgalactic kinematic observations.