On the radial acceleration relation of $\Lambda$CDM satellite galaxies

TL;DR

This paper uses high-resolution simulations within the standard cosmological model to predict the behavior of satellite galaxies' radial acceleration relation, highlighting differences from alternative gravity theories like MOND.

Contribution

It demonstrates that in $\ ext{Lambda}$CDM, satellite galaxies follow the same RAR as brighter galaxies but with larger scatter, contrasting with MOND predictions.

Findings

Satellite galaxies follow the same RAR as brighter galaxies with larger scatter.

The RAR evolves mildly with redshift in simulations.

Host galaxy gravitational field has no effect on the RAR in $\ ext{Lambda}$CDM.

Abstract

The radial acceleration measured in bright galaxies tightly correlates with that generated by the observed distribution of baryons, a phenomenon known as the radial acceleration relation (RAR). Dwarf spheroidal satellite galaxies have been recently found to depart from the extrapolation of the RAR measured for more massive objects but with a substantially larger scatter. If confirmed by new data, this result provides a powerful test of the theory of gravity at low accelerations that requires robust theoretical predictions. By using high-resolution hydrodynamical simulations, we show that, within the standard model of cosmology ($\Lambda$CDM), satellite galaxies are expected to follow the same RAR as brighter systems but with a much larger scatter which does not correlate with the physical properties of the galaxies. In the simulations, the RAR evolves mildly with redshift. Moreover, the acceleration due to the gravitational field of the host has no effect on the RAR. This is in contrast with the External Field Effect in Modified Newtonian Dynamics (MOND) which causes galaxies in strong external fields to deviate from the RAR. This difference between $\Lambda$CDM and MOND offers a possible way to discriminate between them.