0 Assigned ID: 6591 ----- Attempting Submission 1 (Thu Apr 10 18:27:28 GMT 2025) ----- HST Phase I Proposal 6591 successfully submitted. Receipt: # 6591-1 Updated observing plan to use MirrorB/PSA for IC1613-B3. -1184895607 ----- Attempting Submission 1 (Wed Aug 13 04:04:26 GMT 2025) ----- HST Phase II Proposal 18074 successfully submitted. Receipt: # 18074-1 ----- Attempting Submission 2 (Mon Dec 08 04:44:56 GMT 2025) ----- HST Phase II Proposal 18074 successfully submitted. Receipt: # 18074-2 ----- Attempting Submission 3 (Mon Jan 26 05:41:32 GMT 2026) ----- Very low metallicity galaxies are a frontier in modern astrophysics. Locally, they represent the exreme low mass end of galaxy formation. At early cosmic time, when the global metallicity is lower, they are the result of some of the earliest galaxy formation in the universe. Despite their importance on a range of scales, understanding the formation and evolution of such galaxies - including the connection between their chemical and physical properties - is a significant challenge due to their generally low masses and/or high redshifts. There is a disparity between observed star formation in low metallicity galaxies and the most common models of star formation inferred from more numerous observations of higher metallicity, often higher mass, galaxies. As a result, the mechanism and medium for star formation in less metal-enriched galaxies is uncertain. A primary constraint can be placed on the nature of star formation using directly measured molecular hydrogen abundance. To date, this has been a challenge since absorption spectroscopy, by necessity, covers only a limited angular extent toward a sometimes ionizing background source. This pilot program capitalizes on the molecular and atomic lines in the HST COS FUV bands to, in conjunction with archival 21 cm emission maps, obtain spatially resolved molecular hydrogen content along two sightines in IC1613. IC1613 is one of best-studied low metallicity galaxies, providing a unique testbed for star formation models. These observations will: (1) extend UV absorption constraints of H2 to external galaxies and (2) place initial constraints on the nature and regulation of star formation in low metallicity galaxies. This is a pilot program to use HST COS to obtain spatially resolved molecular hydrogen measurements in absorption along two individual sightlines toward FUV-bright stars. The approved observing program involves two individual spectroscopic pointings, one for each star, with G130M (and central wavelength of 1096AA). A total of 26 orbits are approved with 11 orbits on one target and 15 orbits for the second to ensure consistent signal-to-noise ratios for both targets. Both targets are in a nearby galaxy, and IC1613-A13 is in a less dense environment, while IC1613-B3 is in a more crowded environment that necessitates careful acquisition. PI A. Polzin is principally responsible for carrying out the proposed analysis. She will work with co-PI's H.-W. Chen and Z. Qu on COS data reduction and analysis. She will work with Co-I's A. V. Kravtsov, N. Gnedin, and V. Semenov on comparisons with outputs from numerical simulations. Co-PI's H.-W. Chen and Z. Qu are experts in observations of the gas in and around galaxies using absorption spectroscopy. They have extensive experience with HST/COS spectra in the last five years, and co-PI H.-W. Chen has developed software for the reduction and analysis of UV spectroscopy from HST. These tools include interfaces for the improvement of the COS wavelength calibration and identification and characterization of absorbers. These tools will expedite the reduction and analysis of the requested spectroscopic data. Co-I's A. V. Kravtsov, N. Gnedin, and V. Semenov are leading theorists in simulations of galaxies and star formation and gas content. Co-I's A. V. Kravtsov and N. Gnedin have developed some of the most established and trusted atomic-to-molecular hydrogen transition models and PI A. Polzin developed an updated model with them. Co-I V. Semenov has specifically worked on the spatial decorrelation between cold gas and young stars due to stellar feedback. We will use these state-of-the-art simulations and models to help interpret our observations of the molecular hydrogen abundance in IC 1613. Galaxies Stellar Populations and the Interstellar Medium 6 false true false false false false SUPPORTED STAR MAIN SEQUENCE O NO Coordinates from HST GO-12587 J2000 J2000 STAR B0-B2 III-I NO Coordinates from WFC3 F275W image. J2000 J2000 COS/FUV Spectroscopic No No G130M 1055 COS/FUV Spectroscopic No No G130M 1096 COS/FUV Spectroscopic No No G130M 1055 COS/FUV Spectroscopic No No G130M 1096 1769405977633 /private/var/folders/z4/0z0plfnn1s7fxvtsh_70vwyh0000gn/T/OPVisit11927252735746979164.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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