Heated Disc Stars in the Stellar Halo

TL;DR

This study uses high-resolution simulations to show that minor galaxy mergers can eject disk stars into the stellar halo, indicating that some halo stars originate from the galaxy's own disk rather than external sources.

Contribution

The paper demonstrates through simulations that minor mergers can dynamically eject disk stars into the stellar halo, revealing a potential internal origin of some halo stars.

Findings

3-5 x 10^8 solar masses of disk stars ejected beyond 5 kpc

Approximately 1% of local disk stars are kinematically halo-like

Inner stellar halos may contain ancient disk stars from past mergers

Abstract

Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM cosmology. We use high-resolution simulations of Galaxy-analogue systems to show that these mergers can dynamically eject disk stars into a diffuse light component that resembles a stellar halo both spatially and kinematically. For a variety of orbital configurations, we find that ~3-5e8 M_sun of primary stellar disk material is ejected to a distance larger than 5 kpc above the galactic plane. This ejected contribution is similar to the mass contributed by the tidal disruption of the satellite galaxy itself, though it is less extended. If we restrict our analysis to the approximate solar neighborhood in the disk plane, we find that ~1% of the initial disk stars in that region would be classified kinematically as halo stars. Our results suggest that the inner parts of galactic stellar halos contain ancient disk stars and that these stars may have been liberated in the very same events that delivered material to the outer stellar halo.