Contributions to the accreted stellar halo: an atlas of stellar deposition

TL;DR

This study uses N-body simulations to analyze how satellite mass, infall time, and orbit shape influence the distribution and kinematics of stars in the accreted stellar halo, revealing mass-dependent deposition patterns.

Contribution

It provides a detailed analysis of how satellite properties affect stellar deposition in the halo, highlighting the roles of mass, infall timing, and orbital characteristics.

Findings

More massive satellites deposit stars deeper into the host potential.

Early accretion contributes mainly to the inner halo regions.

Massive satellites lose angular momentum and become radially anisotropic.

Abstract

The accreted component of stellar halos is composed of the contributions of several satellites, falling onto their host with their different masses, at different times, on different orbits. This work uses a suite of idealised, collisionless N-body simulations of minor mergers and a particle tagging technique to understand how these different ingredients shape each contribution to the accreted halo, in both density and kinematics. I find that more massive satellites deposit their stars deeper into the gravitational potential of the host, with a clear segregation enforced by dynamical friction. Earlier accretion events contribute more to the inner regions of the halo; more concentrated subhaloes sink deeper through increased dynamical friction. The orbital circularity of the progenitor at infall is only important for low-mass satellites: dynamical friction efficiently radialises the most massive minor mergers erasing the imprint of the infall orbit for satellite-to-host virial mass ratios $\gtrsim1/20$. The kinematics of the stars contributed by each satellite is also ordered with satellite mass: low-mass satellites contribute fast-moving populations, in both ordered rotation and radial velocity dispersion. In turn, contributions by massive satellites have lower velocity dispersion and lose their angular momentum to dynamical friction, resulting in a strong radial anisotropy.