Proper Motions in the Andromeda Subgroup

TL;DR

This paper reports VLBI measurements of proper motions of M33 and IC10 galaxies, providing their velocities relative to the Milky Way, which aids in understanding the dynamics and mass distribution of the Local Group.

Contribution

It presents the first direct proper motion measurements of M33 and IC10 using VLBI, offering new data for modeling the Local Group's dynamics.

Findings

M33 moves at 190 +/- 59 km/s relative to the Milky Way.

IC10 moves at 215 +/- 42 km/s relative to the Milky Way.

Results inform models of dark matter halos in the Local Group.

Abstract

This article presents results of VLBI observations of regions of H2O maser activity in the Local Group galaxies M33 and IC10. Since all position measurements were made relative to extragalactic background sources, the proper motions of the two galaxies could be measured. For M33, this provides this galaxy's three dimensional velocity, showing that this galaxy is moving with a velocity of 190 +/- 59 km\s relative to the Milky Way. For IC10, we obtain a motion of 215 +/- 42 km/s relative to the Milky Way. These measurements promise a new handle on dynamical models for the Local Group and the mass and dark matter halo of Andromeda and the Milky Way.