Stellar Mass Segregation in Dark Matter Halos

TL;DR

This study investigates how stellar mass segregation occurs in dark matter halos due to collisional relaxation, using N-body simulations to understand its effects on stellar distributions and implications for galaxy classification.

Contribution

It provides the first detailed simulation-based analysis of stellar mass segregation in dark matter halos, highlighting its impact on stellar distributions and binary formation.

Findings

Low-mass stars become more extended than high-mass stars over 10 Gyr.

Weak tides do not significantly affect mass segregation, but strong tides enhance low-mass star stripping.

Mass segregation increases the number of massive binaries in dwarf galaxy centers.

Abstract

We study the effect of stellar mass segregation driven by collisional relaxation within the potential well of a smooth dark matter halo. This effect is of particular relevance for old stellar systems with short crossing times, where small collisional perturbations accumulate over many dynamical timescales. We run collisional $N$-body simulations tailored to the ambiguous stellar systems Ursa Major 3/Unions 1, Delve 1 and Eridanus 3, modelling their stellar populations as two-component systems of high- and low-mass stars, respectively. For Ursa Major 3/Unions 1 (Delve 1), assuming a dynamical-to-stellar mass ratio of 10, we find that after 10 Gyr of evolution, the radial extent of its low-mass stars will be twice as large as (40 per cent larger than) that of its high-mass stars. We show that weak tides do not alter this relative separation of half-light radii, whereas for the case of strong tidal fields, mass segregation facilitates the tidal stripping of low-mass stars. We further find that as the population of high-mass stars contracts and cools, the number of dynamically formed binaries within that population increases. Our results call for caution when using stellar mass segregation as a criterion to separate star clusters from dwarf galaxies, and suggest that mass segregation increases the abundance of massive binaries in the central regions of dark matter-dominated dwarf galaxies.