A universal velocity dispersion profile for pressure supported systems: evidence for MONDian gravity across 7 orders of magnitude in mass

Abstract

For any MONDian extended theory of gravity where the rotation curves of spiral galaxies are explained through a change in physics rather than the hypothesis of dark matter, a generic dynamical behavior is expected for pressure supported systems: an outer flattening of the velocity dispersion profile occurring at a characteristic radius, where both the amplitude of this flat velocity dispersion and the radius at which it appears are predicted to show distinct scalings with the total mass of the system. By carefully analyzing the dynamics of globular clusters and elliptical galaxies, we are able to significantly extend the astronomical diversity of objects in which MONDian gravity has been tested, from spiral galaxies, to the much larger mass range covered by pressure supported systems. We show that a universal projected velocity dispersion profile accurately describes various classes of pressure supported systems, and further, that the expectations of extended gravity are met, across seven orders of magnitude in mass. These observed scalings are not expected under dark matter cosmology, and would require particular explanations tuned at the scales of each distinct astrophysical system.

Accepted for publication in ApJ, 11 pages, 5 figures 1 table

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