0 Assigned ID: 3422 ----- Attempting Submission 1 (Fri Mar 25 19:02:18 GMT 2022) ----- The circumgalactic medium (CGM) around galaxies is the place where inflows from the intergalactic medium (IGM) and outflows from galaxies interact. Cosmological simulations have predicted that 1) due to the ionizing extragalactic UV background, the low-density IGM has a minimum temperature, which is positively correlated with density and 2) in the higher density CGM, metal-line cooling is balanced by heating from gravitational shocks and galactic feedback, which results in a minimum temperature that anti-correlates with density. As a result of the Hubble expansion, the turnover separating the IGM from the CGM is dependent on redshift. The existence of a minimum temperature strongly influences the manner in which fresh gas accretes onto galaxies, controlling star formation efficiency and mediating galaxy evolution. We propose to observationally determine the minimum temperature of the cool IGM and CGM at z=0-0.5. Observationally, the minimum linewidth and the column density of H I can be used as a proxy for a minimum temperature and density. From a consistent Voigt profile fitting analysis, we will measure linewidths and column densities of about 16,000 H I absorption lines in about 550 COS archival AGN spectra at log N(H I)=13-17, sampling the IGM and the outer CGM at z=0-0.5. From this large, well-defined dataset, we will (1) determine the turnover density and the CGM temperature-density relation and compare them with predictions; (2) estimate the implied sizes of the CGM and (3) trace the evolution of the IGM and CGM by combining the proposed low-redshift measurement with observations at z=2.4. The PI Dr. Tae-Sun Kim has extensive experience with analyzing QSO spectra taken with both space-based and ground-based spectrographs (COS, STIS, FUSE, UVES, HIRES), especially in terms of data reduction and the Voigt profile fitting analysis. She has led three HST GO/AR proposals and was CoI on five additional ones. She has authored 10 and co-authored about 45 papers on physical conditions in the intergalactic medium (IGM) and circumgalactic medium (CGM). Dr. Bart Wakker has extensive background in studies of the interstellar and intergalatic medium. He has published over 100 papers on these subjects, using data from ground-based radio and optical telescopes, as well as many of the UV space instruments (IUE, FUSE, FOS, GHRS, STIS, COS), being PI on 11 HST GO and 4 HST AR projects, as well as Co-PI or Admin-PI on 7 others. Prof. Blair Savage has specialized in UV spectroscopic studies of the physical state of the ISM and IGM from the very beginning of UV space astronomy. His UV observational studies have utilized the OAO-2, the Copernicus satellite, IUE, GHRS, FOS, STIS, COS and FUSE. He has been involved in 260 refereed publications describing ISM and IGM results. In recent years he has concentrated his efforts on determing the properties and the physical processes operating in the highly ionized ISM, IGM and CGM. Prof. Robert Carswell is the creator of the publicly available Voigt profile fitting program VPFIT which is highly regarded and widely used in the IGM/CGM community. He has extensive experience on data reduction and analysis using both optical and UV QSO spectra. He has led numerous IGM/CGM research projects and is an expert on the IGM evolution, the DLA studies and photoionization modeling. Prof. Martin Haehnelt has led many high-profile, international theoretical projects regarding IGM evolution, galactic feedback and supermassive black holes. He has extensive experience on analytical modeling and numerical simulations. He will help coordinate the research direction in terms of theoretical and analytical aspects of the project as well as the interpretation of the data. Prof. Lindsay King has extensive expertise in analyzing and interpreting cosmological simulations including baryonic physics, and comparing simulations with observations. Of particular relevance to this project, she has assessed the impact of various prescriptions for physical processes such as AGN feedback on mass density and gravitational lensing properties. She is an expert on gravitational lensing with general expertise in galaxy formation and evolution, and large-scale structure. Prof. Matteo Viel is a theoretical expert on the evolution of the IGM and the large-scale structure. He has been working on the properties of the IGM and the interaction between the IGM and galaxies by combining astrophysical theories, various simulations and observational data. In particular he has been studying the impact of different heating mechanisms on the IGM/CGM temperature. Prof. James Bolton is a leading theorist on the IGM temperature and the UV background radiation field. He is the PI of the Sherwood IGM simulation project (https://www.nottingham.ac.uk/astronomy/sherwood/). With his extensive work on simulations, his contribution to the project will include comparing data with predictions from various cosmological simulations as well as extracting physical constraints from observational results. Mr. Ben Rosenwasser is a graduate student at UW-Madison who is working on a number of projects analyzing absorption line data, focusing especially on photoionization models and characterizing associated galaxies with absorbers. Intergalactic Medium and the Circumgalactic Medium 0 Regular false false true false false false SUPPORTED