The "Building Blocks" of Stellar Halos

TL;DR

This paper uses cosmological simulations to explore how the properties of stellar halos relate to their most massive progenitors, revealing that halo populations resemble those of present-day dwarf galaxies.

Contribution

It demonstrates a connection between stellar halo characteristics and the properties of their main progenitors using hydrodynamical simulations.

Findings

Stellar populations in halos resemble old populations in dwarf galaxies.

Median metallicity of halos is linked to the mass of the most massive progenitor.

Progenitors would resemble dwarf irregulars if not accreted.

Abstract

The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the APOSTLE project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass $\sim 0.2-0.5$ dex greater than that of the stellar halo. This suggest that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.