The halo mass dependence of physical and observable properties in the circumgalactic medium at z = 0

We study the dependence of the physical and observable properties of the circumgalactic medium on its halo mass in 25 high resolution cosmological ‘zoom-in’ simulations from the Auriga suite. We focus on the current epoch (z = 0) and on halo masses of 10¹⁰\, M≤ M_200 c≤ 10¹² M⊙ and stellar masses of 107 M⊙ ≤ M⋆ ≤ 1011 M⊙. The mass resolution of our simulations is 5.4 × 103 M⊙. This work analyses the temperature, density, metallicity and radial velocity of these haloes and the column density of H i, Mg ii, Si ii, C iv and O vi. We find median temperature and metallicity increase with halo mass as expected. We find a larger scatter in temperature at higher halo masses, suggesting that the multiphase nature of the CGM is halo mass dependent. Our H i column densities show good agreement with observations at all radii. Mg ii and Si ii match observations between 0.1R200c-0.3R200c, but decrease steeply with radius. O vi column densities are underpredicted by our simulations for stellar masses between 109.5 M⊙ ≤ M⋆ < 1010.2 M⊙ at large radii with reasonable agreement at 1011 M⊙. C iv column densities agree with observational detections above a halo mass of 109.5M⊙. We find that O vi (H i) traces the highest (lowest) temperatures, and lowest (highest) density and metallicity. O vi (C iv) is photo-ionized (collisionally ionized) at low (high) halo masses with a transition to higher temperatures at 1011 M⊙. Our results demonstrate similarities and discrepancies between simulations of Milky Way-mass haloes and observations. They also show further observational constraints are needed in less massive haloes.