Reading the CARDs: the Imprint of Accretion History in the Chemical Abundances of the Milky Way's Stellar Halo

Abstract

In the era of large-scale spectroscopic surveys in the Local Group (LG), we can explore using chemical abundances of halo stars to study the star formation and chemical enrichment histories of the dwarf galaxy progenitors of the Milky Way (MW) and M31 stellar halos. In this paper, we investigate using the Chemical Abundance Ratio Distributions (CARDs) of seven stellar halos from the Latte suite of FIRE-2 simulations. We attempt to infer galaxies' assembly histories by modelling the CARDs of the stellar halos of the Latte galaxies as a linear combination of "template" CARDs from disrupted dwarfs, with different stellar masses M and quenching times t 100 . We present a method for constructing these templates using present-day dwarf galaxies. For four of the seven Latte halos studied in this work, we recover the mass spectrum of accreted dwarfs to a precision of < 10%. For the fraction of mass accreted as a function of t 100 , we find residuals of 20-30% for five of the seven simulations. We discuss the failure modes of this method, which arise from the diversity of star formation and chemical enrichment histories dwarf galaxies can take. These failure cases can be robustly identified by the high model residuals. Though the CARDs modeling method does not successfully infer the assembly histories in these cases, the CARDs of these disrupted dwarfs contain signatures of their unusual formation histories. Our results are promising for using CARDs to learn more about the histories of the progenitors of the MW and M31 stellar halos.

Coupling Semi-Analytic and N-body Galaxies (CoSANG) for cosmological stellar halo simulations I- Methods and the structure of dark matter halos

“…m12b and m12f demonstrate differences between DMO and CoSANG as one might expect; however m12i raises the question why it shows a different behavior to the two As discussed in section 5.2, m12i is a late forming halo and has a different merger history compared to m12b and m12f. This difference is reported in other similar studies of simulations that use the same initial conditions, where capturing the unusual accretion history of m12i becomes a challenge (Cunningham et al 2021). SAMs are sensitive to the merger history of the halo and this difference can The residual is the orientation of the axis at each radial bin (A in blue, B in red, and C in green) relative to the orientation of that axis in the innermost bin in both DMO (dashed) and CoSANG (solid), The haloes have a relatively consistent orientation at all distances.…”

The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars

“…In this situation, the chemical abundances of stars are the only fossil records of the physical conditions of the star formation in the galaxies at different epochs. Therefore, by making an analysis of the chemical abundance patterns of resolved stellar populations in the halo combined together with the phase-space data one could extract precise information about the galactic building blocks (Font et al 2006;Cunningham et al 2021;Deason et al 2016;Roederer et al 2018;Helmi 2020).…”