The halo mass dependence of physical and observable properties in the circumgalactic medium

Abstract

We study the dependence of the physical and observable properties of the CGM on its halo mass. We analyse 22 simulations from the Auriga suite of high resolution cosmological `zoom-in' simulations at $z=0$ with halo masses $10^{10}~\text{M}_{\odot}\leq\text{M}_{\mathrm{200c}}\leq10^{12}~\text{M}_{\odot}$. We find a larger scatter in temperature and smaller scatter in metallicity in more massive haloes. The scatter of temperature and metallicity as a function of radius increases out to larger radii. The median and scatter of the volume-weighted density and mass-weighted radial velocity show no significant dependence on halo mass. Our results highlight that the CGM is more multiphase in haloes of higher mass. We additionally investigate column densities for HI and the metal ions CIV, OVI, MgII and SiII as a function of stellar mass and radius. We find the HI and metal ion column densities increase with stellar mass at sufficiently large radii ($R\gtrsim{0.2}$R$_{\mathrm{200c}}$). We find good agreement between our HI column densities and observations outside $20$% of the virial radius and overpredict within $20$%. MgII and SiII are similarly overpredicted within $20$% of the virial radius, but drop off steeply at larger radii. Our OVI column densities underpredict observations for stellar masses between $10^{9.7}~\text{M}_{\odot}\leq\text{M}_{\star}<10^{10.8}~\text{M}_{\odot}$ with reasonable agreement at $10^{10.8}~\text{M}_{\odot}$. CIV column densities agree with observational detections above a halo mass of $10^{9.7}~\text{M}_{\odot}$. We find that OVI (MgII) traces the highest (lowest) temperatures, and lowest (highest) density and metallicity. OVI and CIV are photo-ionized (collisionally ionized) at low (high) halo masses with a transition to higher temperatures at $10^{11}~\text{M}_{\odot}$. However, there is no clear trend for the radial velocity of the ions.