Probing dark matter and galaxy evolution with proper motions of galaxies

TL;DR

Measuring galaxy proper motions with next-generation radio arrays can reveal detailed cluster dynamics, galaxy infall histories, and merger speeds, advancing our understanding of dark matter and galaxy evolution.

Contribution

This paper proposes using upcoming radio telescope capabilities to measure galaxy proper motions, providing new insights into cluster dynamics and galaxy evolution.

Findings

Proper motions can determine galaxy orbits in clusters.

Proper motions can identify first infall galaxies.

Proper motions can measure merger speeds.

Abstract

We discuss several problems that can be solved by measuring the proper motions of galaxies in clusters of galaxies, something that should be feasible in the Next Generation Very Large Array era. First, in the Virgo Cluster, the Laser Interferometric Space-based Antenna should provide standard siren distances for a substantial number of galaxies which contain black hole-black hole binaries. Measuring the proper motions of these galaxies will give 6-dimensional phase space information about the orbits of these galaxies, providing a unique set of tracers of cluster dynamics. Additionally, in other clusters proper motion measurements should allow the determination of whether spiral galaxies are on their first infall into the cluster, and measurements of the proper motions of galaxies in merging clusters will allow direct measures of the speed of the merger, which can then be compared with estimates from shocks.