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

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).

24 pages, 7 figures, 7 tables. Accepted in MNRAS

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• NGC 3741: dark halo profile from the most extended rotation curve
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• Will-Nordtvedt PPN formalism applied to renormalization group extensions of general relativity
• Solar System constraints on Renormalization Group extended General Relativity: The PPN and Laplace-Runge-Lenz analyses with the external potential effect
• Core and Halo Properties in Multi-Field Wave Dark Matter
• Testing non-local gravity through Ultra-Diffuse Galaxies kinematics
• Velocity dispersion of dark matter deficient ultra-diffuse galaxies: A case for modified gravity
• Low-mass disc galaxies and the issue of stability: MOND vs dark matter
• A framework for creating galaxy models in the geometry of the conservation group with dark matter halos and flat rotation curves
• Structure-wide dark matter density depletion induced by local degeneracies