Virial theorem in clusters of galaxies with MOND
Abstract
A specific modification of Newtonian dynamics known as MOND has been shown to reproduce the dynamics of most astrophysical systems at different scales without invoking nonbaryonic dark matter (DM). There is, however, a longstanding unsolved problem when MOND is applied to rich clusters of galaxies in the form of a deficit (by a factor around two) of predicted dynamical mass derived from the virial theorem with respect to observations. In this article, we approach the virial theorem using the velocity dispersion of cluster members along the line of sight rather than using the cluster temperature from Xray data and hydrostatic equilibrium. Analytical calculations of the virial theorem in clusters for Newtonian gravity + DM and MOND are developed, applying pressure (surface) corrections for nonclosed systems. Recent calibrations of DM profiles, baryonic ratio, and baryonic (β model or others) profiles are used, while allowing free parameters to range within the observational constraints. It is shown that solutions exist for MOND in clusters that give similar results to Newton + DM  particularly in the case of an isothermal β model for β = 0.550.70 and core radii r_{c} between 0.1 and 0.3 times r_{500} (in agreement with the known data). The disagreements found in previous studies seem to be due to the lack of pressure corrections (based on inappropriate hydrostatic equilibrium assumptions) and/or inappropriate parameters for the baryonic matter profiles.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2022
 DOI:
 10.1093/mnras/stac3117
 arXiv:
 arXiv:2210.13961
 Bibcode:
 2022MNRAS.517.5734L
 Keywords:

 gravitation;
 galaxies: clusters;
 dark matter;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 accepted to be published in MNRAS