The formation of hot gaseous haloes around galaxies

TL;DR

This study uses cosmological simulations to explore how hot gaseous haloes form around galaxies, identifying key mass thresholds and the impact of feedback mechanisms like supernovae and AGN on hot gas accumulation.

Contribution

It introduces a combined simulation and analytic approach to determine the critical halo mass for hot halo formation, highlighting feedback effects on hot gas content.

Findings

Hot haloes form in halos of mass $10^{11.5}-10^{12} M_ ext{sun}$ across redshifts 0-4.

AGN feedback reduces hot gas mass, while supernova winds increase it.

The critical halo mass for hot halo formation is approximately $10^{11.7} M_ ext{sun}$ at z=0.

Abstract

We use a suite of hydrodynamical cosmological simulations from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) project to investigate the formation of hot hydrostatic haloes and their dependence on feedback mechanisms. We find that the appearance of a strong bimodality in the probability density function (PDF) of the ratio of the radiative cooling and dynamical times for halo gas provides a clear signature of the formation of a hot corona. Haloes of total mass $10^{11.5}-10^{12}{\rm{M}}_{\odot}$ develop a hot corona independent of redshift, at least in the interval $z=0-4$ where the simulation has sufficiently good statistics. We analyse the build up of the hot gas mass in the halo, $M_{\rm{hot}}$, as a function of halo mass and redshift and find that while more energetic galactic winds powered by SNe increases $M_{\rm{hot}}$, AGN feedback reduces it by ejecting gas from the halo. We also study the thermal properties of gas accreting onto haloes and measure the fraction of shock-heated gas as a function of redshift and halo mass. We develop analytic and semianalytic approaches to estimate a `critical halo mass', $M_{\rm{crit}}$, for hot halo formation. We find that the mass for which the heating rate produced by accretion shocks equals the radiative cooling rate, reproduces the mass above which haloes develop a significant hot atmosphere. This yields a mass estimate of $M_{\rm{crit}} \approx 10^{11.7}{\rm{M}}_{\odot}$ at $z=0$, which agrees with the simulation results. The value of $M_{\rm{crit}}$ depends more strongly on the cooling rate than on any of the feedback parameters.