Galactic Tides and the Outer Density Profile of the Sculptor and Ursa Minor Dwarf Spheroidals
Year: 2026
Type: article
Abstract: Most dwarf spheroidal (dSph) satellites of the Milky Way follow exponential surface density profiles that decline sharply in the outer regions. The Sculptor (Scl) and Ursa Minor (UMi) dSphs deviate from this trend and show a clear excess of stars in the outskirts. Individual members have recently been identified as far as ∼10 effective radii from the center in both systems. We study whether far-outlying stars in Scl and UMi may result from Galactic tidal forces using idealized N -body simulations. Our results indicate that, on their current orbits, neither galaxy has experienced tidal forces strong enough to affect its stellar density profile. The observed velocity dispersion and size of Scl and UMi imply that these dwarfs are simply too dense to have been affected by Galactic tides. Our conclusions do not change when including the effects of the Large Magellanic Cloud, which, according to our simulations, substantially perturbed Scl’s orbit during a recent, close encounter. Our results are insensitive to assumptions about the detailed dark matter density profile of either galaxy, including the presence of an inner core. We conclude that the outlying stars in Scl or UMi are not of tidal origin, but rather innate features that possibly reflect past merger events or the presence of multiple dynamical components.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, National Aeronautics and Space Administration, University of Victoria, Innovation, Science and Economic Development Canada, Space Telescope Science Institute, European Space Agency, Durham University, University of Toronto, Alliance de recherche numérique du Canada, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council
Awards: G1021425983, G103270039, G1338664626, Durham DiRAC-2 petascale facility, G1468651527, G1599146377, DiRAC-2.5 - the pathway to DiRAC Phase 3, G2309215924, G2368581224, G256731684, G2843074508, G3363198467, G4251892262, G4498713678, G4831232377, G4848836895, G5385953647, G5568641063, DiRAC-2.5 DC - Operations 2017-2020, Collaborative Research: Dwarf Galaxies Over Cosmic Time, The Milky Way and its neighbours in the era of large surveys, DiRAC: Memory Intensive 2.5y, G8104139569, DiRAC: Memory Intensive 2.5x
OpenAlex ID: W7157697660