MOND and the Mass Discrepancies in Tidal Dwarf Galaxies

Abstract

I consider in light of MOND the three debris galaxies discussed recently by Bournaud et al.. These exhibit mass discrepancies of a factor of a few within several scale lengths of the visible galaxy, which, arguably, flies in the face of the cold dark matter paradigm. I show here that the rotational velocities predicted by MOND agree well with the observed velocities for each of the three galaxies, with only the observed baryonic matter as the source of gravity. There is thus no need to invoke a new form of baryonic, yet-undetected matter that dominates the disc of spiral galaxies, as advocated by Bournaud et al. I argue on other grounds that the presence of such ubiquitous disc dark matter, in addition to cold dark matter, is not likely.