Inflow of low-metallicity cool gas in the halo of the Andromeda galaxy

Andrea Afruni,Filippo Fraternali,Gabriele Pezzulli

doi:10.1093/mnras/stab3237

Andrea Afruni, Filippo Fraternali + Show 1 more

Open Access

https://doi.org/10.1093/mnras/stab3237

Copy DOI

Abstract

ABSTRACT As the closest L* galaxy to our own Milky Way, the Andromeda galaxy (M31) is an ideal laboratory for studies of galaxy evolution. The AMIGA project has recently provided observations of the cool (T ∼ 104 K) phase of the circumgalactic medium (CGM) of M31, using HST/COS absorption spectra along ∼40 background QSO sightlines, located up to and beyond the galaxy virial radius. Based on these data, and by the means of semi-analytic models and Bayesian inference, we provide here a physical description of the origin and dynamics of the cool CGM of M31. We investigate two competing scenarios, in which (i) the cool gas is mostly produced by supernova(SN)-driven galactic outflows or (ii) it mostly originates from infall of gas from the intergalactic medium. In both cases, we take into account the effect of gravity and hydrodynamical interactions with a hot corona, which has a cosmologically motivated angular momentum. We compare the outputs of our models to the observed covering factor, silicon column density and velocity distribution of the AMIGA absorbers. We find that, to explain the observations, the outflow scenario requires an unphysically large (&gt; 100%) efficiency for SN feedback. Our infall models, on the other hand, can consistently account for the AMIGA observations and the predicted accretion rate, angular momentum and metallicity are consistent with a cosmological infall from the intergalactic medium.

Highlights

The Andromeda galaxy (M31) is our closest external L∗ galaxy and represents an ideal laboratory for galaxy evolution studies, in many respects even more than our own Milky Way (MW)
We have found that in the ETGs the cool circumgalactic medium (CGM) is well reproduced by an inflow of clouds falling at a rate consistent with the accretion predicted by cosmological models; for star-forming galaxies we investigated instead the impact of galactic feedback on the surrounding CGM, finding that supernova driven galactic winds cannot reproduce the cool absorbers observed at distances of hundreds of kpc from the central galaxy, given the unphysical energy requirements that this scenario would imply
We conclude that SN driven galactic outflows are not a viable way to reproduce the majority of the cool gas observed in the halo of M31. This is in line with the main result of AFP21, where we found that galactic winds cannot reproduce the cool CGM of a sample of about 40 lowredshift star-forming galaxies

Summary

Introduction

The Andromeda galaxy (M31) is our closest external L∗ galaxy and represents an ideal laboratory for galaxy evolution studies, in many respects even more than our own Milky Way (MW). A significant amount of baryons seems to reside in the CGM (e.g. Gatto et al 2013; Werk et al 2014) and, the role of this medium is believed to be crucial for the growth and evolution of galaxies. This gas can be used to study both the accretion of gas towards the galaxy (e.g. Kereš et al 2009) and the effect of feedback on the galactic environment (e.g. Nelson et al 2019).

Objectives

Results

Discussion

Conclusion