Journal Article

The survival of dynamical fossils in dwarf spheroidal galaxies in conventional and modified dynamics

F. J. Sánchez-Salcedo and V. Lora

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 2, pages 1135-1147
Published in print September 2010 | ISSN: 0035-8711
Published online September 2010 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2010.16963.x
The survival of dynamical fossils in dwarf spheroidal galaxies in conventional and modified dynamics

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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 was found to be fully satisfactory. Our conclusion is that the cold clump in UMi poses a challenge for both Lambda cold dark matter (ΛCDM) and MOND.

Keywords: gravitation; galaxies: individual: Ursa Minor dSph; galaxies: kinematics and dynamics; galaxies: star clusters: general; dark matter

Journal Article.  9841 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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