AR 16607 (Archival Research)

Sun Jul 14 20:00:56 GMT 2024

Principal Investigator: Jane Charlton
PI Institution: The Pennsylvania State University
Investigators (xml)

Title: Is There a Relationship Between the Metallicity of the Circumgalactic Medium and the Galaxy Orientation?
Cycle: 29

The circumgalactic medium (CGM) of a galaxy is shaped through inflows of pristine and recycled material and by outflows from starburst and AGN activity. Theoretical expectations are for metallicities in galaxy halos to be higher along the minor axis than along the major axis. However, previous studies have failed to identify a significant trend of this type, despite some indirect suggestions that it should be there. We hypothesize that the trend is "washed out" by methods of metallicity determination that associate all of the HI with the low ionization gas. More sophisticated models have demonstrated that a typical CGM sightline passes through a complex multi-phase, multi-cloud medium, with metallicities sometimes differing by up to 1-2 orders of magnitude between different phases/clouds. We propose an archival analysis of 47 absorption line systems produced by lines of sight through the CGM of galaxies at z<0.7 with known impact parameters and orientations. The analysis will use the photoionization code, CLOUDY, and a cloud-by-cloud, multiphase Bayesian method to separate out the phases along the line of sight, and place formal constraints on metallicity, density, and temperature for all the different gaseous structures. This method has been demonstrated to agree with simulation data, and several of the systems have been analyzed as a proof of concept. We expect either to confirm expectations of higher metallicities along the minor axis in some of the components, or to reveal a higher level of mixing and complexity than expected. Either way it will inform the needed sub-grid physics for next generation cosmological hydrodynamic simulatons of the CGM.