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Peer-reviewedCC BY 4.0The Astrophysical Journal

Galactic Tides and the Outer Density Profile of the Sculptor and Ursa Minor Dwarf Spheroidals

  • Daniel A. Boyea1
  • Julio F. Navarro1,2
  • Jaclyn Jensen1,3
  • Raphaël Errani4
4 affiliations
  1. 1University of Victoria
  2. 2Korea University
  3. 3Department of Physics and Astronomy
  4. 4Carnegie Mellon University
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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.

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Cite

BibTeXRIS
BibTeX
@article{boyea2026galactic,
  title = {{Galactic Tides and the Outer Density Profile of the Sculptor and Ursa Minor Dwarf Spheroidals}},
  author = {Daniel A. Boyea and Julio F. Navarro and Jaclyn Jensen and Raphaël Errani},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea600},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea600},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Galactic Tides and the Outer Density Profile of the Sculptor and Ursa Minor Dwarf Spheroidals
AU  - Daniel A. Boyea
AU  - Julio F. Navarro
AU  - Jaclyn Jensen
AU  - Raphaël Errani
PY  - 2026
DA  - 2026/10/09
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea600
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea600
AB  - 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.
SN  - 0004-637X
SN  - 1538-4357
ER  -