The proper motion of the Local Group galaxy IC 10

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: brunthal@mpifr-bonn.mpg.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Department of Astrophysics, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL Nijmegen, The Netherlands

Received: 22 September 2006
Accepted: 25 October 2006

Abstract

We have measured the proper motion of the Local Group galaxy IC 10 with the Very Long Baseline Array by measuring the position of an H₂O maser relative to two background quasars over 4.3 years. After correction for the rotation of the Milky Way and IC 10, we obtain a motion of – μas yr^-1 toward the East and  μas yr^-1 toward the North. This corresponds to a total space velocity of  km s^-1 relative to the Milky Way for an assumed distance of  kpc. Assuming that IC 10 and M 33, for which also a proper motion measurement exists, are bound to M 31, we calculate a lower limit for the mass of M 31 of  .