The radial acceleration relation in a $\Lambda$CDM universe

TL;DR

This study analytically and numerically investigates the radial acceleration relation (RAR) in a $ m extbf{ extLambda}$CDM universe, revealing how baryonic feedback and dark matter distribution shape the RAR across different acceleration regimes.

Contribution

It introduces an analytical framework linking RAR to dark matter relaxation physics and demonstrates the effectiveness of a simple baryonification model in reproducing observed RAR features.

Findings

The RAR in high-acceleration regimes is sensitive to relaxation physics details.

A baryonification model accurately reproduces observed RAR without tuning.

In low-acceleration regimes, the RAR depends on diffuse gas abundance, predicting a break in the relation.

Abstract

We study the radial acceleration relation (RAR) between the total ($a_{\rm tot}$) and baryonic ($a_{\rm bary}$) centripetal acceleration profiles of central galaxies in the cold dark matter (CDM) paradigm. We analytically show that the RAR is intimately connected with the physics of the quasi-adiabatic relaxation of dark matter in the presence of baryons in deep potential wells. This cleanly demonstrates how the mean RAR and its scatter emerge in the low-acceleration regime ($10^{-12}\,{\rm m\,s}^{-2}\lesssim a_{\rm bary}\lesssim10^{-10}\,{\rm m\,s}^{-2}$) from an interplay between baryonic feedback processes and the distribution of CDM in dark halos. Our framework allows us to go further and study both higher and lower accelerations in detail, using analytical approximations and a realistic mock catalog of $\sim342,000$ low-redshift central galaxies with $M_r\leq-19$. We show that, while the RAR in the baryon-dominated, high-acceleration regime ($a_{\rm bary}\gtrsim10^{-10}\,{\rm m\,s}^{-2}$) is very sensitive to details of the relaxation physics, a simple `baryonification' prescription matching the relaxation results of hydrodynamical CDM simulations is remarkably successful in reproducing the observed RAR without any tuning. And in the (currently unobserved) ultra-low-acceleration regime ($a_{\rm bary}\lesssim 10^{-12}\,{\rm m\,s}^{-2}$), the RAR is sensitive to the abundance of diffuse gas in the halo outskirts, with our default model predicting a distinctive break from a simple power-law-like relation for HI-deficient, diffuse gas-rich centrals. Our mocks also show that the RAR provides more robust, testable predictions of the $\Lambda$CDM paradigm at galactic scales, with implications for alternative gravity theories, than the baryonic Tully-Fisher relation.