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arXiv · 2209.06229

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

Nikolay Kacharov·Mayte Alfaro-Cuello·Nadine Neumayer·Nora Lützgendorf·Laura L. Watkins·Alessandra Mastrobuono-Battisti·Sebastian Kamann·Glenn van de Ven·Anil C. Seth·Karina T. Voggel·Iskren Y. Georgiev·Ryan Leaman·Paolo Bianchini·Torsten Böker·Steffen Mieske
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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.

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Nikolay Kacharov, Mayte Alfaro-Cuello, Nadine Neumayer, Nora Lützgendorf, Laura L. Watkins, Alessandra Mastrobuono-Battisti, Sebastian Kamann, Glenn van de Ven, Anil C. Seth, Karina T. Voggel, Iskren Y. Georgiev, Ryan Leaman, Paolo Bianchini, Torsten Böker, Steffen Mieske. 2022-09-13. 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. https://doi.org/10.3847/1538-4357%2Fac9280

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