AR 17027 (Archival Research)

Sun Jul 14 11:31:16 GMT 2024

Principal Investigator: Tae-Sun Kim
PI Institution: University of Wisconsin - Madison
Investigators (xml)

Title: Thermal properties of the IGM and CGM: Confronting simulations with observations
Cycle: 30

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.