Where are the Population III Star Relics in the Simulated Milky Way Analogs?

Abstract Using six Milky Way analogs with two different numerical resolutions from the Auriga simulation, we investigate the total mass, spatial distribution, and kinematics of the Population III (Pop III) star relics in the Milky Way analogs at z = 0. These relics (primarily second-generation stars) formed over a wide redshift range, from about z = 22 to z = 4, with an average formation redshift of z ∼ 10.0, and comprise about 2 × 10 −5 of the entire galactic stellar population. The disk and bulge components host only a small fraction of these relics, contributing less than 12% in total. The stellar halo, in particular the outer stellar halo of galactic radius r > 30 kpc, hosts the largest fraction (about 46% on average), with an average of one relic star per 4000 to 10,000 stars, making it a promising region for observational searches. Additionally, around 18% of the Pop III star relics are found in satellite galaxies, with smaller and older satellite galaxies tending to contain a higher proportion of these stars. Thus, low-mass and early-formed satellite galaxies are also ideal targets for finding such relics, although some satellite galaxies may lack them entirely. The spatial distribution and kinematics of these stars show good numerical convergence across different simulation resolutions. Our results provide valuable guidance for searches of the Pop III star relics and offer insights for interpreting findings from ongoing and future stellar archaeology surveys.