The mass discrepancy acceleration relation in early-type galaxies: extended mass profiles and the phantom menace to MOND

TL;DR

This study investigates the mass discrepancy acceleration relation in early-type galaxies, finding similarities to spiral galaxies but with systematic offsets, challenging the universality of the relation and implications for dark matter and MOND theories.

Contribution

It extends the analysis of the MDA relation to early-type galaxies using homogeneous dynamical models, revealing deviations from spiral galaxy patterns.

Findings

Early-type galaxies follow a similar MDA relation to spirals but are systematically offset.

Mass density profiles are consistent with MOND expectations on average, but some individual discrepancies exist.

The results challenge the universality of the MDA relation and its implications for dark matter and modified gravity theories.

Abstract

The dark matter (DM) haloes around spiral galaxies appear to conspire with their baryonic content: empirically, significant amounts of DM are inferred only below a universal characteristic acceleration scale. Moreover, the discrepancy between the baryonic and dynamical mass, which is usually interpreted as the presence of DM, follows a very tight mass discrepancy acceleration (MDA) relation. Its universality, and its tightness in spiral galaxies, poses a challenge for the DM interpretation and was used to argue in favour of MOdified Newtonian Dynamics (MOND). Here, we test whether or not this applies to early-type galaxies. We use the dynamical models of fast-rotator early-type galaxies by Cappellari et al. based on ATLAS$^{3D}$ and SLUGGS data, which was the first homogenous study of this kind, reaching ~4 $R_e$, where DM begins to dominate the total mass budget. We find the early-type galaxies to follow an MDA relation similar to spiral galaxies, but systematically offset. Also, while the slopes of the mass density profiles inferred from galaxy dynamics show consistency with those expected from their stellar content assuming MOND, some profiles of individual galaxies show discrepancies.