A Study of Stars in the Sagittarius Dwarf Spheroidal Galaxy

Abstract

The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph) is one of the closest known satellite galaxies of the Milky Way. It is currently being tidally disrupted by and merging with our galaxy; the Milky Way grows by accreting smaller galaxies and globular clusters, and Sgr dSph is an insight into the process through which this occurs. Knowledge of the stellar population of Sgr dSph will aid our understanding of the stellar content seen in the Milky Way and how it will evolve in the future - characterising the stellar population of Sgr dSph is the main aim of this project. The Python Stellar Spectral Energy Distributions (PySSED) programme - designed to fit stellar parameters to stars through spectral energy distribution (SED) fitting - was used to create HR diagrams of multiple fields spread across the body of Sgr dSph, with Gaia DR3 being used as the primary source of data. Isochrones were fitted to each of the HR diagrams in order to gain information about the age and metallicity of the stellar population in each field, allowing the observation of variations in these properties across the galaxy. It was found that in agreement with other research, an age-metallicity relationship was present, with older stellar populations tending to be more metal-rich. There was also some evidence of the previously suggested age-metallicity gradient - where the stellar population of Sgr dSph becomes older and more metal-poor as radius from the centre of the galaxy increases - although this was not definitive. Outlier objects that had been identified were investigated in more depth to see if any interesting objects in Sgr dSph could be discovered. While none of the objects or their membership of Sgr dSph can be identified with certainty, some potentially interesting objects that may belong to Sgr dSph were found, including possible hot subdwarfs, post-AGB and planetary nebula candidates, and Mira variables. These objects must be examined in greater detail in order to decide whether they are a part of Sgr dSph and what their true identity is.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Albert Zijlstra (Supervisor) & Keith Grainge (Supervisor)