The Dual Origin of Stellar Halos II: Chemical Abundances as Tracers of Formation History

TL;DR

This study uses advanced cosmological simulations to analyze chemical abundance patterns in stellar halos, revealing differences based on star origin and merger history, which align with recent Milky Way observations.

Contribution

It demonstrates how chemical abundance trends can distinguish between in situ and accreted stars in stellar halos using high-resolution simulations.

Findings

In situ stars are more alpha-rich at high [Fe/H] than accreted stars.

Chemical abundance patterns reflect the formation environment and merger history.

Results match observations of local Milky Way halo stars.

Abstract

Fully cosmological, high resolution N-Body + SPH simulations are used to investigate the chemical abundance trends of stars in simulated stellar halos as a function of their origin. These simulations employ a physically motivated supernova feedback recipe, as well as metal enrichment, metal cooling and metal diffusion. As presented in an earlier paper, the simulated galaxies in this study are surrounded by stellar halos whose inner regions contain both stars accreted from satellite galaxies and stars formed in situ in the central regions of the main galaxies and later displaced by mergers into their inner halos. The abundance patterns ([Fe/H] and [O/Fe]) of halo stars located within 10 kpc of a solar-like observer are analyzed. We find that for galaxies which have not experienced a recent major merger, in situ stars at the high [Fe/H] end of the metallicity distribution function are more [alpha/Fe]-rich than accreted stars at similar [Fe/H]. This dichotomy in the [O/Fe] of halo stars at a given [Fe/H] results from the different potential wells within which in situ and accreted halo stars form. These results qualitatively match recent observations of local Milky Way halo stars. It may thus be possible for observers to uncover the relative contribution of different physical processes to the formation of stellar halos by observing such trends in the halo populations of the Milky Way, and other local L* galaxies.