Chemodynamical analyses of the Milky Way satellites Sagittarius II and Aquarius II with GHOST: challenges in detecting dark matter in ultra-faint systems
| dc.contributor.author | Zaremba, Daria | |
| dc.contributor.supervisor | Venn, Kimberley Ann | |
| dc.date.accessioned | 2025-08-29T17:45:15Z | |
| dc.date.available | 2025-08-29T17:45:15Z | |
| dc.date.issued | 2025 | |
| dc.degree.department | Department of Physics and Astronomy | |
| dc.degree.level | Master of Science MSc | |
| dc.description.abstract | Deep photometric surveys have revealed numerous faint Milky Way satellites with absolute V-band magnitudes Mv ≳−5. Distinguishing whether these systems are dark matter-dominated ultra-faint dwarf galaxies (UFDs) or purely baryonic globular clusters (GCs) remains a key challenge. In this thesis, we explore the diagnostic power of detailed chemical abundances using high-resolution Gemini/GHOST spectra of five stars in two low surface brightness satellites – Sagittarius II (Sgr2) and Aquarius II (Aqu2). For Aqu2, the kinematics and metallicities of two stars support a dark matter-dominated UFD origin. The abundance patterns – low Na, Sr, Ba, and enhanced K – indicate inefficient star formation from only a few supernovae, possibly with enrichment from super-AGB stars. In contrast, Sgr2 shows unresolved velocity and metallicity dispersions, and its stars exhibit typical metal-poor abundance ratios with little spread. One exception is the discovery of an r-process-enhanced star (Sgr2584, [Eu/Fe] = +0.7 ±0.2), which does not clarify its nature, as such stars are found in both UFDs (Tuc III, Tuc IV, Grus II) and GCs (M15 and M92). However, radial mass segregation offers modest support for a GC classification. Motivated by this ambiguity, we examine the “Valley of Ambiguity“ – the region below MV ≲−5 in the size–luminosity (rh-Mv) plane – by dividing it into five zones of shared properties. We identify observational caveats and propose diagnostics to address UFD–GC overlap in each. We argue that only a multi-faceted approach – combining kinematic (e.g., velocity dispersions of member stars, tidal streams kinematics), dynamical (e.g., tidal resilience, mass function slopes, detections of mass segregation), and chemical diagnostics (e.g., metallicity spreads, heavy elemental deficiencies, carbon enhancement) – offers the most robust path to classification. Coupled with N-body modeling, this strategy is essential for interpreting ambiguous systems in the era of large-scale photometric and spectroscopic surveys. | |
| dc.description.scholarlevel | Graduate | |
| dc.identifier.uri | https://hdl.handle.net/1828/22683 | |
| dc.language | English | eng |
| dc.language.iso | en | |
| dc.rights | Available to the World Wide Web | |
| dc.subject | the Milky Way | |
| dc.subject | Dwarf galaxies | |
| dc.subject | Star clusters | |
| dc.subject | Stellar abundances | |
| dc.subject | Astronomical instrumentation | |
| dc.title | Chemodynamical analyses of the Milky Way satellites Sagittarius II and Aquarius II with GHOST: challenges in detecting dark matter in ultra-faint systems | |
| dc.type | Thesis |