The Radial Acceleration Relation (RAR): the crucial cases of Dwarf Discs and of Low Surface Brightness galaxies

Chiara Di Paolo, Paolo Salucci

Published 2018-10-19Version 1

McGaugh et al. (2016) have found, in a large sample of disc systems, a tight nonlinear relationship between the total radial accelerations $g$ and their components $g_b$ arisen from the distribution of the baryonic matter ~\citep{McGaugh_2016}. Here, we investigate the existence of such relation in Dwarf Disk Spirals and Low Surface Brightness galaxies on the basis of ~\cite{Karukes_2017} and ~\cite{DiPaolo_2018}. 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 one order of magnitude below the smallest accelerations present in McGaugh et al. (2016) and span different Hubble Types. We found, in our samples, that the $g$ vs $g_b$ relation has a very different profile and also other intrinsic novel properties among those the dependence on a second variable: the galactic radius normalised to the optical radius $R_{opt}$, at which the two accelerations are calculated. We show that the new complex $g$ vs $(g_b, r/R_{opt})$ relationship is not else that a direct consequence of the complex mass distribution in galaxies. Our analysis shows that the McGaugh et al. (2016) relation is a limiting case of our new complex universal relation and can be interpreted in the standard "DM halo in the Newtonian Gravity" paradigm.