Testing Modified Newtonian dynamics through statistics of velocity dispersion profiles in the inner regions of elliptical galaxies

TL;DR

This study tests Modified Newtonian Dynamics (MOND) against observed velocity dispersion profiles in elliptical galaxies, finding that MOND can successfully reproduce empirical data without dark matter, unlike Newtonian models.

Contribution

It demonstrates that MOND, with a suitable interpolating function, can match the velocity dispersion slope distribution in elliptical galaxies without requiring dark matter.

Findings

MOND reproduces observed VDP slope distribution in elliptical galaxies.

Newtonian dynamics with dark matter needs galaxy-specific dark matter profiles.

Statistical analysis of VDPs can constrain MOND models.

Abstract

Modified Newtonian dynamics (MOND) provides a paradigm alternative to dark matter that has been successful in fitting and predicting the rich phenomenology of rotating disc galaxies. There have also been attempts to test MOND in dispersion-supported early-type galaxies, but it remains unclear whether MOND can fit the various empirical properties of early-type galaxies. As a way of rigorously testing MOND in elliptical galaxies we calculate the MOND-predicted velocity dispersion profiles (VDPs) in the inner regions of $\sim 2000$ nearly round SDSS elliptical galaxies under a variety of assumptions on VD anisotropy, and then compare the predicted distribution of VDP slopes with the observed distribution in 11 ATLAS3d galaxies selected with essentially the same criteria. We find that the MOND model parameterised with an interpolating function that works well for rotating galaxies can also reproduce the observed distribution of VDP slopes based only on the observed stellar mass distribution without DM or any other galaxy-to-galaxy varying factor. This is remarkable in view that Newtonian dynamics with DM requires a specific amount and/or profile of DM for each galaxy in order to reproduce the observed distribution of VDP slopes. When we analyse non-round galaxy samples using the MOND-based spherical Jeans equation, we do not find any systematic difference in the mean property of the VDP slope distribution compared with the nearly round sample. However, in line with previous studies of MOND through individual analyses of elliptical galaxies, varying MOND interpolating function or VD anisotropy can lead to systematic change in the VDP slope distribution, indicating that a statistical analysis of VDPs can be used to constrain specific MOND models with an accurate measurement of VDP slopes or a prior constraint on VD anisotropy.