Figuring Out Gas & Galaxies in Enzo (FOGGIE). XV. Examining the Spatial and Kinematic Relationship between Circumgalactic Mg II and O VI

Abstract

Understanding the thermodynamic properties of the circumgalactic medium (CGM) is key to uncovering the baryon cycle in galaxies. Here we present spatial and kinematic relationships between Mg II and O VI as representatives for low and high ion-bearing gas, in the cosmological zoom-in galaxy simulation suite FOGGIE, a set of Milky-way-like galaxy simulations with high CGM resolution. We find the O VI-bearing gas exists as a diffuse halo around the galactic disk, while the Mg II-bearing gas is more centrally located. We investigate the covering fraction, probability of co-observation, co-kinematic correspondence of these ions using two different analysis methods. We make both mock sightlines using two-dimensional projections of our simulations treating these cells as integrated lines of sight and we create one-dimensional ray objects and use the SALSA (Boyd et al. 2020) code to investigate individual gas structures that contribute most to the line of sight column densities, which we call mock absorbers. We explore the relative kinematics of these mock absorbers and find Mg II and O VI appear to have a co-kinematic relationship when looking at absorber pairs with the closest relative velocity like in Werk et al. (2016). However, this does not necessarily correspond with a close spatial separation meaning many O VI and Mg II absorber pairs only appear to be co-kinematic but are physically unrelated. Taking a more holistic look at Mg II and O VI absorber pairs reveals a much weaker correlation between these two ions.