0 Assigned ID: 661 ----- Attempting Submission 1 (Fri Apr 05 19:28:17 GMT 2019) ----- HST Phase I Proposal 661 (UV-only Metallicities.apt) successfully submitted. Receipt: # 661-1 ----- Attempting Submission 2 (Fri Apr 05 19:53:14 GMT 2019) ----- We propose a new technique for determining gas-phase metallicity measurements in the Galactic halo that is independent of beam-smearing effects. Beam smearing effects result from combining radio 21 cm HI emission measurements with UV metal-absorption measurements. This can lead to systematic errors in metallicity estimates that prevent accurate comparisons to theoretical predictions and extragalactic measurements. Our new technique instead uses Far Ultraviolet Spectroscopic Explorer (FUSE) data covering the full Lyman absorption series to measure HI without relying on 21 cm observations. Our pilot study finds systematically lower HI columns from UV measurements than from 21 cm measurement. When combining with HST measurements of metals, the preliminary results indicate that the metallicity of Galactic halo clouds could be underestimated by at least a factor of 2. Here we propose to confirm these potentially important results via an analysis of 41 archival HST COS or STIS sightlines with complementary FUSE and 21 cm radio data. We propose measurements of OI 1302 and SII 1259, 1253, 1250 absorption from which we will measure the oxygen and sulfur abundances in IVCs and HVCs with both UV and radio HI measurements. With this sample we will quantify the reliability of radio-based metallicities. If confirmed, the offset between radio-derived and UV-derived metallicities would have significant implications on the origin of HVCs and IVCs and on how these local structures relate to extragalactic circumgalactic absorbers. The PI Dr David French has just finished a PhD thesis based on data from HST COS and STIS, studying the Lyman alpha absorption lines associated with nearby galaxies. He is an expert in UV data fitting, analysis, and interpretation. He will lead the FUSE and HST COS/STIS absorption profile modeling, abundance measurements, and the final interpretation of the data. Dr Andrew Fox is an expert in the reduction, analysis, and interpretation of FUSE and HST/COS spectra of diffuse gas in the Universe. He has led four HST GO proposals on CGM-related science, all of which have led to refereed publications and NASA press releases, and has first-authored 11 ApJ papers using UV spectroscopy. He will provide guidence on the analysis and help manage the contributions of the Co-Is. Dr Bart Wakker has an extensive background in studies of the interstellar and intergalactic medium, having published over 100 papers on these subjects. He has worked with many of the UV space instruments (IUE, FUSE, FOS, GHRS, STIS, COS), being PI on 11 HST observing and 4 HST archival projects, as well as Co-PI or Admin-PI on 7 others. He also has extensive experience with radio 21 cm emission data of the Galactic Halo. Dr Jason Tumlinson is a highly experienced UV user and global expert in galaxy formation and evolution, and is the PI of the COS-Halos and COS-Dwarfs programs on the CGM. Galaxies and the IGM 0 Regular false false true false false SUPPORTED