Recovering the infall mass for Milky Way satellite galaxy Sextans

TL;DR

This study uses tailored N-body simulations to estimate the infall mass of the Sextans dwarf galaxy, revealing its dark matter content and the effects of tidal interactions, with implications for galaxy formation models.

Contribution

It introduces a novel simulation-based method to recover the infall mass of Sextans, accounting for tidal and baryonic effects, and constrains its dark matter profile and formation history.

Findings

Infall mass of Sextans ranges from 1.22 to 3.14 billion solar masses.

Stars in Sextans are only mildly affected by galactic tides.

Results are consistent with stellar mass-halo mass relations.

Abstract

Understanding the formation and evolution of the Milky Way (MW) requires detailed knowledge of its satellite galaxies. In this study, we focus on the Sextans dwarf spheroidal (dSph) galaxy, a faint, dark matter (DM)-dominated satellite, to investigate the role of tidal and baryonic effects in shaping its observed properties. Using tailored $N$-body simulations, we explore possible orbits of Sextans in different MW models to reconstruct its progenitor's properties. Our simulations demonstrate the stars in Sextans are only mildly affected by galactic tides and the stellar kinematics provide robust constraints on its dynamical mass within the half-light radius, while the tidal mass loss of its DM component depends primarily on MW mass. The recovered infall mass of Sextans ranges from $1.22$ to $3.14\times10^9\rm\,M_\odot$ for MW masses from $0.8$ to $2\times10^{12}\rm\,M_\odot$. If the DM density remained as cuspy as NFW profile, the infall mass would be smaller by a factor of 2. Although with large ranges, the possible infall masses of Sextans recovered by our simulations are consistent with the stellar mass-halo mass relation in TNG50 and abundance matching results. We find some cases for the cuspy DM density profile where the infall mass is smaller than $10^9\rm\,M_\odot$, possibly indicating that star formation in Sextans is more efficient than in other satellites. The recovered DM halo structural parameters from our simulations provide valuable constraints for future studies on the DM content and formation history of Sextans.