Assigned ID: 906 ----- Attempting Submission 1 (Fri Feb 24 23:26:01 GMT 2012) ----- The Milky Way halo is covered with gaseous structures observed through 21-cm emission, and through high, intermediate and low ionization absorption lines. Detailed case studies of individual high velocity clouds have shown them to be multiphase structures, with low ionization metal lines falling through the hot halo and producing high ionization interface layers evident in OVI. Surveys of OVI from FUSE show large coherent structures covering large fractions of the sky, but the structures traced by the low ionization gas have not yet been systematically mapped. Our previous HST/STIS archival study found six low ionization HVCs along 26 sightlines. The HST/COS archive now facilitates an unprecidented study of ten times as many sightlines through the Milky Way halo, mapping a much wider variety of directions, and allowing constraints on transverse sizes. Coverage with the G130M and G160M gratings allows for simultaneous study of SiII 1260, OI 1302, CII 1335, SiIV 1394, and CIV 1548, which allow for a detailed study of the physical conditions of the low/intermediate ionization gas. High velocity clouds are not only important for our understanding of our own galaxy, but also trace the conditions of the gas around galaxies over cosmic time. The critical UV spectra obtained by HST/COS provide the benchmark by which galaxies of a variety of types, and over a wide range of redshifts, can be measured. QUASAR ABSORPTION LINES AND IGM 12 Medium false 0.0 0.0 false false false false SUPPORTED