Visiting non-Newtonian MOND gravity in low-mass galaxies

The consistency of the application of Milgrom's modified dynamics (MOND) is tested in low-mass disc galaxies. If the existing Toomre parameter is a good indicator of axisymmetric instabilities, then catastrophic ring instabilities are predicted to occur in the gas component of dwarf gas-rich galaxies. These dynamical instabilités would promote large gas concentrations and would destroy the smoothness of the disc in a few orbit times. As a rule, the attributed property of MOND to explain that the observed rotation curve is a scaled version of the rotation curve derived from the HI alone, may break down. Decreasing the adopted distance to these galaxies in order to recover gas stability is unsatisfactory. These points are illustrated with the low-mass galaxies IC 2574 and NGC 1560, and with the tidal tail in the interacting galaxies NGC 4485/4490.