The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach

TL;DR

This study uses high-resolution simulations combined with semi-analytic methods to explore the formation and properties of the Milky Way and its stellar halo, revealing insights into their assembly history and metallicity distribution.

Contribution

It introduces a hybrid cosmological approach to model the Galaxy and its halo, explaining the dual nature and metallicity distribution of the stellar halo.

Findings

Major halo contribution from early-accreted massive satellites

No clear metallicity gradient in the stellar halo

Higher metallicity stars are more centrally concentrated

Abstract

We use a series of high-resolution simulations of a `Milky-Way' halo coupled to semi-analytic methods to study the formation of our own Galaxy and of its stellar halo. The physical properties of our model Milky Way, as well as the age and metallicity distribution of stars in the different components, are in relatively good agreement with observational measurements. Assuming that the stellar halo builds up from the cores of the satellite galaxies that merged with the Milky Way over its life-time, we are able to study the physical and structural properties of this component. In agreement with previous work, we find that the largest contribution to the stellar halo should come from a few relatively massive (10^8 - 10^10 Msun) satellites, accreted at early times. Our "stellar halo" does not exhibit any clear metallicity gradient, but higher metallicity stars are more centrally concentrated than stars of lower abundance. This indicates that the probability of observing low-metallicity halo stars increases with distance from the Galactic centre. We find that the proposed "dual" nature of the Galactic stellar halo can be explained in our model as a result of a mass-metallicity relation imprinted in the building blocks of this component.