Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-05-17
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
14 pages, 13 figures, accepted for publication in MNRAS
Scientific paper
The survival of unbound density substructure against orbital mixing imposes strong constraints on the slope of the underlying gravitational potential and provides a new test on modified gravities. Here we investigate whether the interpretation that the stellar clump in Ursa Minor (UMi) dwarf spheroidal galaxy is a `dynamical fossil' is consistent with Modified Newtonian dynamics (MOND). For UMi mass models inferred by fitting the velocity dispersion profile, the stellar clump around the second peak of UMi is erased very rapidly, within 1.25 Gyr (6.5 orbits), even with the inclusion of self-gravity. We find that the clump can hardly survive for more than 2 Gyr even under more generous conditions. Alternative scenarios which could lead to a kinematically cold clump are discussed but, so far, none of them were found to be fully satisfactory. Our conclusion is that the cold clump in UMi poses a challenge for both LambdaCDM and MOND.
Lora V.
Sanchez-Salcedo Javier F.
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