A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. III. Discrete multi-component population-dynamical models based on the Jeans equations

TL;DR

This paper develops multi-component dynamical models of the Sagittarius dwarf galaxy's nucleus using Jeans equations, revealing the mass distribution, stellar population contributions, and their dynamical interplay within M54.

Contribution

It introduces a comprehensive Jeans-based modeling approach that simultaneously fits stellar populations' properties, spatial distributions, and kinematics, advancing understanding of the galaxy's nuclear cluster formation.

Findings

Total mass within M54's tidal radius is approximately 1.6 million solar masses.

Metal-poor globular cluster stars contribute about 65% of the total mass.

Distinct stellar populations are successfully distinguished by their spatial, age, metallicity, and kinematic differences.

Abstract

We present comprehensive multi-component dynamical models of M54 (NGC6715), the nuclear star cluster of the Sagittarius dwarf galaxy (Sgr), which is undergoing a tidal disruption in the Milky Way halo. Previous papers in the series used a large MUSE mosaic data set to identify multiple stellar populations in the system and study their kinematic differences. Here we use Jeans-based dynamical models that fit the population properties (mean age and metallicity), spatial distributions, and kinematics simultaneously. They provide a solid physical explanation to our previous findings. The population-dynamical models deliver a comprehensive view of the whole system, and allow us to disentangle the different stellar populations. We explore their dynamical interplay and confirm our previous findings about the build-up of Sgr's nuclear cluster via contributions from globular cluster stars, Sgr inner field stars, and in-situ star formation. We explore various parameterisations of the gravitational potential and show the importance of a radially varying mass-to-light ratio for the proper treatment of the mass profile. We find a total dynamical mass within M54's tidal radius ($\sim75$ pc) of $1.60\pm0.07\times10^6$ Msun in excellent agreement with $N$-body simulations. The metal-poor globular cluster stars contribute about $65\%$ of the total mass or $1.04\pm0.05\times10^6$ Msun. The metal-rich stars can be further divided into young and intermediate age populations that contribute $0.32\pm0.02\times10^6$ Msun ($20\%$) and $0.24\pm0.02\times10^6$ Msun ($15\%$), respectively. Our population-dynamical models successfully distinguish the different stellar populations in Sgr's nucleus because of their different spatial distributions, ages, metallicities, and kinematic features.