Chemical and Dynamical Properties of the Stellar Halo

TL;DR

This paper investigates the chemical and dynamical differences between stellar populations in the Milky Way's halo, linking their origins to formation history, merger events, and primordial conditions, with implications for understanding Population III stars.

Contribution

It distinguishes halo star populations based on formation time and merger history, and explores their chemical signatures and distribution, providing insights into early galaxy formation and Population III stars.

Findings

Old stars are centrally concentrated, originating from early dense regions.

Primordial stars are distributed throughout the halo, not just centrally.

Metallicity observations constrain Population III initial mass function.

Abstract

The difference in density profiles of the contributions from different density peaks to dark matter halos results in certain expectations about the Milky Way's stellar halo. We cut our simulated halo stars into two populations: those forming before/during the last major merger, and those accreted after the last major merger. The former population are more centrally located at z=0, while stars forming in low mass late forming proto-galaxies are spread through the halo. A difference in observed binding energy distinguishes these two populations. We look at possible chemical abundance signatures of the two populations. We also show that galaxies forming in isolated low sigma peaks will form from primordial material. Thus, even though the oldest stars are centrally concentrated as they originated in the early collapsing, densest regions, primordial stars would be found distributed throughout the halo. Thus, the lack of observed metal free stars can be taken as directly constraining the Population III IMF, and the lowest metallicity observed stars can be interpreted as holding clues to the chemical yields of Pop III stars.