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[72.09] The Infall of Low Metallicity Gas onto the Galactic Disk

B.K. Gibson, S.V. Penton, M.L. Giroux, J.T. Stocke, J.M. Shull (CU/CASA), C. Chiappini (National Obs., Brazil)

We present an HST GHRS+STIS abundance analysis of the High-Velocity Cloud (HVC) Complex~C, seen in absorption toward five background QSOs. The \ion{S}{2} metallicity along the Mrk~290 sightline (0.09\,Z_\odot), line-of-sight velocity (-120\,km\,s^-1), and inferred thermal pressure have motivated the suggestion that Complex~C represents a prototypical example of the postulated source of infalling low metallicity gas that in turn fuels the bulk of star formation in the Milky Way. We discuss how our mapping of the abundance distribution, via the use of what is now five background probes spread across the face of the HVC, affects this picture of Galactic evolution. New multi-episodic HVC infall models governing the formation of the halo and thick+thin disks will be presented.