Cold and Hot gas distribution around the Milky-Way-M31 system in the HESTIA simulations

TL;DR

This study uses high-resolution simulations to analyze the distribution of cold and hot gas around the Milky Way and Andromeda, revealing differences in gas clumpiness and comparing simulation results with observations.

Contribution

It provides the first detailed characterization of CGM gas distributions in the Local Group using the HESTIA simulations, including mock skymaps and power spectra.

Findings

Cold gas tracers are more clumpy than warm gas tracers.

Simulations under-predict M31's CGM column densities but match low-redshift galaxy observations.

Gas contamination from the Milky Way's CGM may affect M31 observations.

Abstract

Recent observations have revealed remarkable insights into the gas reservoir in the circumgalactic medium (CGM) of galaxy haloes. In this paper, we characterise the gas in the vicinity of Milky Way and Andromeda analogues in the HESTIA (High resolution Environmental Simulations of The Immediate Area) suite of constrained Local Group (LG) simulations. The HESTIA suite comprise of a set of three high-resolution {\sc arepo}-based simulations of the LG, run using the Auriga galaxy formation model. For this paper, we focus only on the $z = 0$ simulation datasets and generate mock skymaps along with a power spectrum analysis to show that the distributions of ions tracing low-temperature gas (HI and SiIII) are more clumpy in comparison to warmer gas tracers (OVI, OVII and OVIII). We compare to the spectroscopic CGM observations of M31 and low-redshift galaxies. HESTIA under-produces the column densities of the M31 observations, but the simulations are consistent with the observations of low-redshift galaxies. A possible explanation for these findings is that the spectroscopic observations of M31 are contaminated by gas residing in the CGM of the Milky Way.