Stellar haloes of simulated Milky Way-like galaxies: Chemical and kinematic properties

TL;DR

This study analyzes the chemical and kinematic properties of stellar haloes in simulated Milky Way-like galaxies, revealing distinct populations and their origins, with implications for understanding galaxy formation and evolution.

Contribution

It provides a detailed characterization of inner and outer halo stellar populations, including their origins, chemical properties, and kinematic signatures, based on high-resolution simulations.

Findings

Inner and outer haloes have distinct stellar populations.

Disc-heated stars contribute significantly to the inner halo.

Abundance gradients are shaped by multiple stellar sub-populations.

Abstract

We investigate the chemical and kinematic properties of the diffuse stellar haloes of six simulated Milky Way-like galaxies from the Aquarius Project. Binding energy criteria are adopted to defined two dynamically distinct stellar populations: the diffuse inner and outer haloes, which comprise different stellar sub-populations with particular chemical and kinematic characteristics. Our simulated inner- and outer-halo stellar populations have received contributions from debris stars (formed in sub-galactic systems while they were outside the virial radius of the main progenitor galaxies) and endo-debris stars (those formed in gas-rich sub-galactic systems inside the dark matter haloes). The inner haloes possess an additional contribution from disc-heated stars in the range $\sim 3 - 30 %$, with a mean of $\sim 20% $. Disc-heated stars might exhibit signatures of kinematical support, in particular among the youngest ones. Endo-debris plus disc-heated stars define the so-called \insitu stellar populations. In both the inner- and outer-halo stellar populations, we detect contributions from stars with moderate to low [$\alpha$/Fe] ratios, mainly associated with the endo-debris or disc-heated sub-populations. The observed abundance gradients in the inner-halo regions are influenced by both the level of chemical enrichment and the relative contributions from each stellar sub-population. Steeper abundance gradients in the inner-halo regions are related to contributions from the disc-heated and endo-debris stars, which tend to be found at lower binding energies than debris stars. (Abridged).