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

TL;DR

This study extends the Radial Acceleration Relation to Dwarf Discs and Low Surface Brightness galaxies, revealing a more complex, radius-dependent relation that aligns with standard dark matter halo models.

Contribution

It uncovers a new, radius-dependent universal relation between accelerations in disc galaxies, expanding the understanding of the Radial Acceleration Relation beyond previous findings.

Findings

The $g$ vs $g_b$ relation varies with galactic radius in dwarf and LSB galaxies.

The new relation depends on the normalized galactic radius, $r/R_{opt}$.

The relation supports the standard dark matter halo paradigm.

Abstract

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 [McGaugh_2016]. Here, we investigate the existence of such relation in Dwarf Disc Spirals and Low Surface Brightness galaxies on the basis of [Karukes_2017] and [DiPaolo_2018]. We have accurate mass profiles for 36 Dwarf Disc 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. (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 measured. We show that the new far than trivial $g$ vs $(g_b, r/R_{opt})$ relationship is nothing else than a direct consequence of the complex, but coordinated mass distributions of the baryons and the dark matter (DM) in disc systems. Our analysis shows that the McGaugh et al. (2016) 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.