Letter to the Editor

Tidal dwarf galaxies as a test of fundamental physics

¹ University of New Mexico, Department of Physics and Astronomy, 800 Yale Blvd NE, Albuquerque, NM 87131, USA e-mail: ggentile@unm.edu
² Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
³ LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
⁴ Argelander-Institut für Astronomie (AIfA), Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁵ SUPA, School of Physics and Astronomy, University of St. Andrews, KY16 9SS, Fife, UK

Received: 13 June 2007
Accepted: 11 July 2007

Abstract

Within the cold dark matter (CDM) framework tidal dwarf galaxies (TDGs) cannot contain dark matter, so the recent results by Bournaud et al. (2007, Science, 316, 1166) that 3 rotating TDGs do show significant evidence for being dark matter dominated is inconsistent with the current concordance cosmological theory unless yet another dark matter component is postulated. We confirm that the TDG rotation curves are consistent with Newtonian dynamics only if either an additional dark matter component is postulated, or if all 3 TDGs happen to be viewed nearly edge-on, which is unlikely given the geometry of the tidal debris. We also find that the observed rotation curves are very naturally explained without any free parameters within the modified Newtonian dynamics (MOND) framework if inclinations are adopted as derived by Bournaud et al. We explore different inclination angles and two different assumptions about the external field effect. The results do not change significantly, and we conclude therefore that Newtonian dynamics has severe problems while MOND does exceedingly well in explaining the observed rotation curves of the 3 TDGs studied by Bournaud et al.