The Radial Acceleration Relation (RAR): Crucial Cases of Dwarf Disks and Low-surface-brightness Galaxies

Abstract

Abstract McGaugh et al. have found, in a large sample of disk systems, a tight nonlinear relationship between the total radial accelerations g and their components g b that have arisen from the distribution of the baryonic matter. Here, we investigate the existence of such a relation in Dwarf Disk Spirals and Low Surface Brightness (LSB) galaxies on the basis of Karukes & Salucci and Di Paolo & Salucci. We have accurate mass profiles for 36 Dwarf Disk Spirals and 72 LSB galaxies. These galaxies have accelerations that cover the McGaugh range but also reach out to one order of magnitude below the smallest accelerations present in McGaugh et al. and span different Hubble Types. We found, in our samples, that the g versus g b relation has a very different profile and also other intrinsic novel properties, among those, the dependence on a second variable: the galactic radius, normalized to the optical radius R opt, at which the two accelerations are measured. We show that the new far from trivial g versus relationship is a direct consequence of the complex coordinated mass distributions of the baryons and the dark matter (DM) in disk systems. Our analysis shows that the McGaugh et al. relation is a limiting case of a new universal relation that can be very well framed in the standard “DM halo in the Newtonian Gravity” paradigm.