The morphology and kinematics of neutral hydrogen in the vicinity of z=0 galaxies with Milky Way masses -- a study with the Illustris simulation

TL;DR

This study uses the Illustris simulation to analyze how the morphology and kinematics of neutral hydrogen in the circumgalactic medium vary with gas content in Milky Way-mass galaxies, revealing differences driven by AGN feedback and rotation coherence.

Contribution

It provides new insights into the dependence of CGM properties on gas fraction and feedback processes in Milky Way-like galaxies using high-resolution cosmological simulations.

Findings

Gas-rich galaxies have higher neutral hydrogen column densities extending to 50-70 kpc.

Gas-poor galaxies exhibit rapid temperature increases and asymmetric gas distributions.

Rotational coherence of the CGM varies with gas richness, reaching up to 70-100 kpc in the most gas-rich systems.

Abstract

We analyze the properties of the circumgalactic gas (CGM) around 120 galaxies with stellar and dark matter halo masses similar to that of the Milky Way. We focus on the morphology and kinematics of the neutral hydrogen and how this depends on f_g, the ratio of gas-to-stellar mass within the optical radius. In gas-rich galaxies with f_g > 0.1, gas temperatures rise slowly from center of the halo out to the virial radius and average neutral gas column densities remain above 10^19 atoms cm^-2 out to radii of 50-70 kpc. In gas-poor galaxies with f_g < 0.1, gas temperatures rise quickly outside the edge of the disk to 10^6 K, and then remain fixed out to radii of 100 kpc. The column density of neutral gas quickly drops below 10^19 atoms cm^-2 at radii of 10 kpc. Neutral gas distributions are also more asymmetric in gas-poor galaxies. Most of the differences between gas-poor and gas-rich galaxies in the Illustris simulation can be attributed to the effects of "radio-mode" AGN feedback. In the Illustris simulation, the circumgalactic gas is found to rotate coherently about the center of the galaxy with a maximum rotational velocity of around 200 km/s. In gas-rich galaxies, the average coherence length of the rotating gas is 40 kpc, compared to 10 kpc in gas-poor galaxies. In the very most gas-rich systems, the CGM can rotate coherently over scales of 70-100 kpc. We discuss our results in the context of recent observations of the CGM in low mass galaxies via UV absorption-line spectroscopy and deep 21cm observations of edge-on spiral galaxies.