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Topic

The extended light profiles of the Sculptor and Ursa Minor dwarf galaxies: Innate nature or tidal nurture?

Department of Physics and Astronomy

Date & location

• Tuesday, December 16, 2025
• 9:00 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Julio Navarro, Department of Physics and Astronomy, ӣ��Ӱ�� (Supervisor)
• Dr. Kim Venn, Department of Physics and Astronomy, UVic (Member)

External Examiner

• Dr. Giuseppina Battaglia, Senior Scientist, Instituto de Astrofísica de Canarias

Chair of Oral Examination

• Dr. Roberta Hamme, School of Earth and Ocean Sciences, UVic

Abstract

The satellite galaxies of the Milky Way (MW), except the Magellanic Clouds, are all dwarf spheroidals (dSphs)—gas-free, non-rotating, dark-matter-dominated stellar systems. The light profiles of dSphs typically follow an exponential law, with a sharply declining outer density. Yet systems like the Sculptor (Scl) and Ursa Minor (UMi) dSphs host member stars out to ∼10 effective radii, indicating outer deviations from an exponential law. The origin of these extended profiles is unclear, possibly arising from Galactic tides or intrinsic properties. In this thesis, we review the evidence for extended light profiles in Scl and UMi, validating the Bayesian membership catalogue of Jensen et al. (2024). To evaluate if tides can produce these density features, we conduct idealized N-body simulations of both galaxies in the tidal field of the Milky Way. We find that neither dwarf experiences tides strong enough to affect their stellar distribution. One complication is that Sculptor’s orbit is strongly influenced by the presence of the Large Magellanic Cloud (LMC). Our N-body models still suggest that the combined tides of the LMC and MW are unable to explain Scl’s outer profile. We conclude that the extended light profiles of Scl and UMi are not of tidal origin. They are instead likely innate, possibly explained by past mergers, accretion events, or episodic star formation.