Abstract
We combine HI 21cm observations of the Milky Way, M31, and the local galaxy population with QSO absorption-line measurements to geometrically model the three-dimensional distribution of infalling neutral gas clouds (HVCs) in the extended halos of low-redshift galaxies. We demonstrate that the observed distribution of HVCs around the Milky Way and M31 can be modeled by a radial exponential decline of the mean HI volume filling factor in their halos. Our model suggests a characteristic radial extent of HVCs of R_halo=50 kpc, a total HI mass in HVCs of ~10^8 M_sun, and a neutral-gas-accretion rate of ~0.7 M_sun/yr for M31/Milky-Way-type galaxies. Using a Holmberg-like luminosity scaling of the halo size of galaxies we estimate R_halo=110 kpc for the most massive galaxies. The total absorption-cross section of HVCs at z=0 most likely is dominated by galaxies with total HI masses between 10^8.5 and 10^10 M_sun. Our model indicates that the HI disks of galaxies and their surrounding HVC population can account for 30-100 percent of intervening QSO absorption-line systems with log N(HI)>17.5 at z=0. We estimate that the neutral-gas accretion rate density of galaxies at low redshift from infalling HVCs is dM_HI/dt/dV=0.022 M_sun/yr/Mpc^3, which is close to the measured star-formation rate density in the local Universe. HVCs thus may play an important role for the on-going formation and evolution of galaxies.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
