The Auriga stellar haloes: connecting stellar population properties with accretion and merging history

Abstract

We examine the stellar haloes of the Auriga simulations, a suite of thirty cosmological magneto-hydrodynamical high-resolution simulations of Milky Way-mass galaxies performed with the moving-mesh code arepo. We study halo global properties and radial profiles out to ∼ 150 kpc for each individual galaxy. The Auriga haloes are diverse in their masses and density profiles; mean metallicity and metallicity gradients; ages; and shapes, reflecting the stochasticity inherent in their accretion and merger histories. A comparison with observations of nearby late-type galaxies shows very good agreement between most observed and simulated halo properties. However, Auriga haloes are typically too massive. We find a connection between population gradients and mass assembly history: galaxies with few significant progenitors have more massive haloes, possess large negative halo metallicity gradients and steeper density profiles. The number of accreted galaxies, either disrupted or under disruption, that contribute 90% of the accreted halo mass ranges from 1 to 14, with a median of 6.5, and their stellar masses span over three orders of magnitude. The observed halo mass-metallicity relation is well reproduced by Auriga and is set by the stellar mass and metallicity of the dominant satellite contributors. This relationship is found not only for the accreted component but also for the total (accreted + in-situ) stellar halo. Our results highlight the potential of observable halo properties to infer the assembly history of galaxies.

NIHAO-UHD: The properties of MW-like stellar disks in high resolution cosmological simulations

“…With dotted lines we show the amount of ex-situ stars in the simulations (colored lines) and predicted by the empirical model of Moster et al (2018). In any case, at redshift z = 0 we find a fraction of at most a few percent of ex-situ stars mostly brought into the galaxy at early times before redshift 2 − 1 in good agreement with Moster et al (2018, dotted black line) and results from the AURIGA simulations (Grand et al 2017;Monachesi et al 2019) but somewhat smaller than previous findings (Pillepich et al 2015). This result has strong implications on the presence and possibilities of finding such ex-situ stars in the MW brought in by disrupted satellite galaxies (e.g.…”

Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey

“…In their model, this relation is set by the hierarchical assembly of dark matter halos in conjunction with an empircally-constrained, redshift-dependent stellar masshalo mass relation and an empirical mass-metallicity relation. D' Souza & Bell (2018) and Monachesi et al (2019) presented similar correlations based on the Illustris and Auriga hydrodynamical simulations. These authors compared their models to observations of the stellar halos of the Milky Way (MW), M31, and six galaxies from the GHOSTS Survey (Harmsen et al 2017).…”

The biggest splash

“…• We have inspected examples from the Auriga and Latte suites of Cosmological zoom-in simulations of the Milky Way's formation, finding that example galaxies in both suites produce a Splashlike structure as a result of the interaction of a massive dwarf galaxy with the pre-existing in-situ (typically disc-like) population (in agreement with Bonaca et al 2017;Monachesi et al 2019). We show that the epoch of this major merger can be accurately calculated via two different routes: either relying on the youngest ages of the accreted stars observed locally at redshift z = 0 or using the ages of the metal-rich in-situ stars on retrograde orbits.…”