Forming Galaxies with MOND

TL;DR

This paper uses a spherically symmetric N-body simulation to explore how elliptical galaxies could form early in a MOND universe through dissipationless collapse, revealing relationships between mass, size, and velocity.

Contribution

It demonstrates that MOND can produce elliptical galaxy-like structures with realistic properties via dissipationless collapse, suggesting early formation of massive ellipticals.

Findings

Virialized objects resemble elliptical galaxies

Mass-radius-velocity dispersion relations are consistent with observations

Upper mass limit for gas cloud cooling in MOND

Abstract

Beginning with a simple model for the growth of structure, I consider the dissipationless evolution of a MOND-dominated region in an expanding Universe by means of a spherically symmetric N-body code. I demonstrate that the final virialized objects resemble elliptical galaxies with well-defined relationships between the mass, radius, and velocity dispersion. These calculations suggest that, in the context of MOND, massive elliptical galaxies may be formed early (z > 10) as a result of monolithic dissipationless collapse. Then I reconsider the classic argument that a galaxy of stars results from cooling and fragmentation of a gas cloud on a time scale shorter than that of dynamical collapse. Qualitatively, the results are similar to that of the traditional picture; moreover, the existence, in MOND, of a density-temperature relation for virialized, near isothermal objects as well as a mass-temperature relation implies that there is a definite limit to the mass of a gas cloud where this condition can be met-- an upper limit corresponding to that of presently observed massive galaxies.