Physics of galactic colliders: high speed satellites in LCDM vs MONDian cosmology

TL;DR

This paper compares the frequency of high-speed satellite galaxy encounters in MOND and LCDM cosmologies, finding that such encounters are about four times more common in MOND due to its infinite potential well.

Contribution

It provides the first cosmological simulation-based comparison of high-speed satellite encounters in MOND versus LCDM models, using a rigorous MONDian Poisson solver.

Findings

High-speed satellite encounters are roughly four times more frequent in MOND than in LCDM.

The difference is attributed to the infinite potential well in MOND versus finite in LCDM.

Results support the hypothesis that satellite velocities can discriminate between gravitational theories.

Abstract

The statistics of high speed satellite galaxies, as reported in the recent literature, can be a powerful diagnosis of the depth of the potential well of the host halo, and hence discriminate between competing gravitational theories. Naively one expects that high speed satellites are more common in Modified Newtonian Dynamics (MOND) than in cold dark matter (CDM) since an isolated MONDian system has an infinite potential well, while CDM halos have finite potential wells. In this \textit{Letter} we report on an initial test of this hypothesis in the context of the first generation of cosmological simulations utilising a rigorous MONDian Poisson solver. We find that such high speed encounters are approximately a factor of four more common in MOND than in the concordance $\Lambda$CDM model of cosmic structure formation.