On the fundamentality of the radial acceleration relation for late-type galaxy dynamics

TL;DR

This paper demonstrates that the radial acceleration relation (RAR) is the fundamental and most significant correlation governing late-type galaxy dynamics, with all other correlations deriving from it, challenging standard cosmological models.

Contribution

It establishes the RAR as the primary dynamical correlation in late-type galaxies and shows its uniqueness compared to other relations, impacting galaxy formation theories.

Findings

RAR is the strongest projection of galaxy radial dynamics.

Other correlations derive from the RAR and non-dynamical factors.

The second most significant dynamical relation lacks RAR's features.

Abstract

Galaxies have been observed to exhibit a level of simplicity unexpected in the complex galaxy formation scenario posited by standard cosmology. This is particularly apparent in their dynamics, where scaling relations display much regularity and little intrinsic scatter. However, the parameters responsible for this simplicity have not been identified. Using the Spitzer Photometry & Accurate Rotation Curves galaxy catalogue, we argue that the radial acceleration relation (RAR) between galaxies' baryonic and total dynamical accelerations is the fundamental $1$-dimensional correlation governing the radial (in-disk) dynamics of late-type galaxies. In particular, we show that the RAR cannot be tightened by the inclusion of any other available galaxy property, that it is the strongest projection of galaxies' radial dynamical parameter space, and that all other statistical radial dynamical correlations stem from the RAR plus the non-dynamical correlations present in our sample. We further provide evidence that the RAR's fundamentality is unique in that the second most significant dynamical relation does not possess any of these features. Our analysis reveals the root cause of the correlations present in galaxies' radial dynamics: they are nothing but facets of the RAR. These results have important ramifications for galaxy formation theory because they imply that to explain statistically late-type galaxy dynamics within the disk it is necessary and sufficient to explain the RAR and lack of any significant, partially independent correlation. While simple in some modified dynamics models, this poses a challenge to standard cosmology.