The radial acceleration relation at the EDGE of galaxy formation

Testing its universality in low-mass dwarf galaxies

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
² Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25, D-14476 Potsdam, Germany
³ University of Surrey, Physics Department, Guildford GU2 7XH, UK
⁴ School of Astronomy and Space Science, Nanjing University, Nanjing, Jiangsu 210023, China
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
⁷ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁸ Leiden Observatory, Leiden University, P.O. Box 9513 2300 RA Leiden, The Netherlands
⁹ University of Bath, Department of Physics, Claverton Down, Bath BA2 7AY, UK
¹⁰ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 43 SE-221 00 Lund, Sweden

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 4 September 2025
Accepted: 3 October 2025

Abstract

A tight correlation between the baryonic and observed acceleration of galaxies has been reported over a wide mass range (10⁸ < M_bar/M_⊙ < 10¹¹ M_⊙); this is known as the radial acceleration relation (RAR). This has been interpreted as evidence that dark matter is actually a manifestation of a modified, weak-field gravity theory. In this work, we studied the radially resolved RAR of 12 nearby dwarf galaxies, with baryonic masses in the 10⁴ < M_bar/M_⊙ < 10^7.5 M_⊙ range, using a combination of literature data and data from the MUSE-Faint survey. We used stellar line-of-sight velocities and the Jeans modelling code GRAVSPHERE to infer the mass distributions of these galaxies, allowing us to compute the RAR. We compare the results with the EDGE simulations of isolated dwarf galaxies with similar stellar masses in a Λ cold dark matter cosmology. We find that most of the observed dwarf galaxies lie systematically above the low-mass extrapolation of the RAR. Each galaxy traces a locus in the RAR space that can have a multi-valued observed acceleration for a given baryonic acceleration, while there is significant scatter from galaxy to galaxy. Our results indicate that the RAR does not apply to low-mass dwarf galaxies, and that the inferred baryonic acceleration of these dwarfs does not contain enough information, on its own, to derive the observed acceleration. The simulated EDGE dwarfs behave similarly to the real data, with a higher observed acceleration at a fixed baryonic acceleration than the extrapolated RAR. We show that, in the context of modified, weak-field gravity theories, these results cannot be explained by differential tidal forces from the Milky Way or by the galaxies being far from dynamical equilibrium, since none of the galaxies in our sample seem to experience strong tides. As such, our results provide further evidence of the need for invisible dark matter in the smallest dwarf galaxies.