Gas flows in the circumgalactic medium around simulated high-redshift galaxies

TL;DR

This study uses cosmological zoom simulations to analyze the impact of supernova feedback on the circumgalactic medium of high-redshift galaxies, revealing complex mass exchange and ionization processes.

Contribution

It introduces a new simulation sample that models the CGM around high-redshift galaxies and examines the effects of supernova feedback on gas flows and ionization.

Findings

Supernova feedback drives outflows and reduces inflow rates.

Neutral outflowing hydrogen density declines exponentially with radius.

No fast-moving neutral outflows are predicted in the CGM.

Abstract

We analyse the properties of circumgalactic gas around simulated galaxies in the redshift range z >= 3, utilising a new sample of cosmological zoom simulations. These simulations are intended to be representative of the observed samples of Lyman-alpha emitters recently obtained with the MUSE instrument (halo masses ~10^10-10^11 solar masses). We show that supernova feedback has a significant impact on both the inflowing and outflowing circumgalactic medium by driving outflows, reducing diffuse inflow rates, and by increasing the neutral fraction of inflowing gas. By temporally stacking simulation outputs we find that significant net mass exchange occurs between inflowing and outflowing phases: none of the phases are mass-conserving. In particular, we find that the mass in neutral outflowing hydrogen declines exponentially with radius as gas flows outwards from the halo centre. This is likely caused by a combination of both fountain-like cycling processes and gradual photo/collisional ionization of outflowing gas. Our simulations do not predict the presence of fast-moving neutral outflows in the CGM. Neutral outflows instead move with modest radial velocities (~ 50 kms^-1), and the majority of the kinetic energy is associated with tangential rather than radial motion.