The Dorcha suite: nature, nurture, and the phase-space distribution of the Milky Way’s high-redshift progenitors today

Abstract

Where in the present-day Milky Way should we search for the remnants of its earliest stars? We address this question using the Dorcha (Gaelic for Dark; DUR-uh-khuh) suite: a set of 25 high-resolution, dark-matter-only cosmological zoom-in simulations of Milky Way analogue (MWA) haloes evolved to z=0. Of these, 15 are isolated and the rest are in pairs, similar to the MW and M31. By identifying and tagging the most bound material in high-redshift (z ≥ 5) progenitor haloes – those likely to host early star formation – we track the present-day phase-space distribution of this ancient component. We find that this material is highly centrally concentrated at z=0, with 90–100 per cent residing wit..