Mining the Galactic Halo for Very Metal-Poor Stars

TL;DR

This study combines simulations and analytical methods to analyze the distribution of very metal-poor stars in the Milky Way halo, revealing where these stars are most likely to be found and how their distribution relates to galactic history.

Contribution

It provides new insights into the spatial distribution of metal-poor stars in the Milky Way halo based on combined simulation and semi-analytical modeling.

Findings

Oldest stars are in the innermost regions.

Extremely metal-poor stars are concentrated within 60 kpc.

Outer halo beyond 40 kpc is optimal for searching very metal-poor stars.

Abstract

We study the age and metallicity distribution function (MDF) of metal-poor stars in the Milky Way halo as a function of galactocentric radius by combining N-body simulations and semi-analytical methods. We find that the oldest stars populate the innermost region, while extremely metal-poor stars are more concentrated within r < 60 kpc. The MDF of [Fe/H] < -2 stars varies only very weakly within the central 50 kpc, while the relative contribution of [Fe/H] < -2 stars strongly increases with r, varying from 16% within 7 kpc < r < 20 kpc up to > 40% for r > 20 kpc. This is due to the faster descent of the spatial distribution (as seen from Earth) of the more enriched population. This implies that the outer halo < 40 kpc is the best region to search for very metal-poor stars. Beyond ~ 60 kpc the density of [Fe/H] < -2 stars is maximum within dwarf galaxies. All these features are imprinted by a combination of (i) the virialization epoch of the star-forming haloes, and (ii) the metal enrichment history of the Milky Way environment.