Modified gravity models and the central cusp of dark matter halos in galaxies

TL;DR

This study compares modified gravity models, specifically RGGR and MOND, to the traditional NFW dark matter profile in fitting galaxy rotation curves, finding that modified gravity can match or outperform NFW in certain regions with fewer parameters.

Contribution

It extends the analysis of RGGR to a larger galaxy sample and compares its effectiveness to MOND and NFW profiles in fitting rotation curves.

Findings

RGGR and MOND fit well below half the disk scale length.

RGGR achieves better overall fits than MOND.

RGGR nearly matches NFW in fit quality with fewer free parameters.

Abstract

The N-body dark matter (DM) simulations point that DM density profiles, e.g. the NFW halo, should be cuspy in its center, but observations disfavour this kind of DM profile. Here we consider whether the observed rotation curves "close" to the galactic centre can favour modified gravity models in comparison to the NFW halo, and how to quantify such difference. Two explicit modified gravity models are considered, MOND and a more recent approach called RGGR (in reference to Renormalization Group effects in General Relativity). It is also the purpose of this work to significantly extend the sample on which RGGR has been tested in comparison to other approaches. By analysing 62 galaxies from five samples, we find that: i) there is a radius, given by half the disk scale length, below which RGGR and MOND can match the data about as well or better than NFW, albeit the formers have fewer free parameters; ii) considering the complete rotation curve data, RGGR could achieve fits with better agreement than MOND, and almost as good as a NFW halo with two free parameters (NFW and RGGR have respectively two and one more free parameters than MOND).