THE DIRECT DETECTION OF COOL, METAL-ENRICHED GAS ACCRETION ONTO GALAXIES AT z ∼ 0.5

We report on the discovery of cool gas inflow toward six star-forming galaxies with redshifts z similar to 0.35-1. Analysis of MgII and Fe II resonance-line absorption in Keck/LRIS spectroscopy of the galaxies reveals positive velocity shifts for cool gas of 80-200 km s(-1) with respect to the host galaxy velocity centroids, and equivalent widths for this inflow of greater than or similar to 0.6 angstrom in five of the six objects. The host galaxies exhibit a wide range of star formation rates (SFRs similar to 1-40 M-circle dot yr(-1)) and have stellar masses similar to that of the Milky Way (log M-*/M-circle dot similar to 9.6-10.5). Imaging from the Hubble Space Telescope Advanced Camera for Surveys indicates that five of the six galaxies have highly inclined (i > 55 degrees), disk-like morphologies. These data represent the first unambiguous detection of inflow into isolated, star-forming galaxies in the distant universe. We suggest that the inflow is due to the infall of enriched material from dwarf satellites and/or a galactic fountain within the galaxies. Assuming that the material has been enriched to 0.1Z(circle dot) and has a physical extent approximately equal to that of the galaxies (implied by the high observed gas covering fractions), we infer mass inflow rates of dM(in)/dt greater than or similar to 0.2-3 M-circle dot yr(-1) for four of these systems. Finally, from comparison of these absorption lines to the profiles of MgII and Fe II absorption in a larger spectroscopic sample of similar to 100 objects, we measure a covering fraction of cool inflow of at least 6%, but cannot rule out the presence of enriched infall onto as many as similar to 40 of these galaxies.