Page numbers start with 1. 1830556658 Assigned ID: 1460 ----- Attempting Submission 1 (Sun Apr 04 15:44:49 GMT 2021) ----- HST Phase I Proposal 1460 successfully submitted. Receipt: # 1460-1 ----- Attempting Submission 2 (Mon Apr 05 18:00:48 GMT 2021) ----- HST Phase I Proposal 1460 successfully submitted. Receipt: # 1460-2 ----- Attempting Submission 3 (Tue Apr 06 19:49:19 GMT 2021) ----- HST Phase I Proposal 1460 successfully submitted. Receipt: # 1460-3 ----- Attempting Submission 4 (Fri Apr 09 12:38:01 GMT 2021) ----- The circumgalactic medium (CGM) of Milky Way-mass galaxies houses as much baryonic and metal mass as that found in the central galaxies themselves, and a majority of the CGM mass is in the form of cool/warm ionized gas (log T ~ 4-6). This ionized phase is shaped by energetic feedback from stars and AGN in both circumgalactic and interstellar gases. Understanding the physical mechanisms that dictate the conditions of this gas and drive its dynamics is critical for understanding how the evolution of galaxies is dictated by the multiphase CGM and ISM. It has become increasingly clear that the physical scale of structures in this gas is an important clue to understanding the evolution of an ionized medium, though it has been very difficult to observationally constrain the scales of CGM/ISM structures. We propose to use the ULLYSES database of STIS and COS observations to study variations in foreground Milky Way column densities of Al III, Si IV, C IV, N V, and O VI (with complementary FUSE data) between pairs of sight lines in the Small and Large Magellanic Clouds. Our analysis will include 10s, 100s, and 1000s of pairs separated by 0.01, 0.1, and 1 deg or less, probing the variation of physical scales from ~1 pc to ~3 kpc. We will assess the scale of variations at radial velocities that highlight gas in the disk, thick disk, and more distant CGM of the Milky Way and assess the scale of variations for gas having narrow b-values representing cool gas separately from gas with broad b-values representing collisionally-ionized gas. Our analysis will probe cloud sizes at the scales expected from recent theoretical models of gas fragmentation or "shattering." The PI Howk and CoI Lehner have over 2 decades of experience analyzing HST UV and FUSE spectra, including from the instrument STIS E140H/M, E230M/H and COS G130M/G160M/G185M. Of particular relevance, the PI has led the first analysis of the angular scale in the Milky Way using the SMC and LMC stars as background objects. The PI and CoI are experts in analyzing interstellar absorption in stellar spectra, including supergiant early-type stars. They have led successfully several large programs to study the Milky disk and halo as well as the gas of the the LMC. These studies have used as UV background objects hot stars of all types and are well-versed in the complexities in estimating stellar continuum placement in the regions that are the focus of this program. Their work includes one of the key STIS programs in the Milky Way that motivated part this program, the Lehner+ (2011) work on profile fitting of gas in the Milky Way disk. They are both specialists in studying the high ions and multi-phase gas in the Milky Way, Magellanic Clouds, and in the low and high redshift universe. CoI Tuli (a graduate student at Notre Dame) has already working experience analyzing low and high ions stellar spectra as part of one of our other HST STIS and FUSE program on the Milky Way's Perseus Arm. The proposed research program will be principally overseen by the PI Howk and CoI Lehner at the University of Notre Dame. The detailed work of the program will be led by both CoIs Lehner and Tuli. This survey will be part of her PhD thesis. CoI Tuli has already working experience analyzing low and high ions stellar spectra as part of one of our other HST STIS and FUSE program. They will both will lead the basic data reduction as well as the bulk of the analysis and interpretation of the results. Each senior member of our team has led large surveys or similarly large efforts as the one proposed here in a timely manner. Each member has been the PI of several GO, archival, and theory HST programs. Our team has published several tens of papers on these topics over the last 10+ years in major scientific journals, including Science and Nature. Stellar Populations and the Interstellar Medium Intergalactic Medium and the Circumgalactic Medium 0 Regular false false true false false SUPPORTED