The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33)
Andreas Brunthaler,1,2*
Mark J. Reid,3
Heino Falcke,4,5
Lincoln J. Greenhill,3
Christian Henkel1
We measured the angular rotation and proper motion of the Triangulum
Galaxy (M33) with the Very Long Baseline Array by observing
two H
2O masers on opposite sides of the galaxy. By comparing
the angular rotation rate with the inclination and rotation
speed, we obtained a distance of 730 ± 168 kiloparsecs.
This distance is consistent with the most recent Cepheid distance
measurement. M33 is moving with a velocity of 190 ± 59
kilometers per second relative to the Milky Way. These measurements
promise a method to determine dynamical models for the Local
Group and the mass and dark-matter halos of M31, M33, and the
Milky Way.
2 Joint Institute for Very Long Baseline Interferometry in Europe, Postbus 2, 7990 AA Dwingeloo, Netherlands.
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
4 ASTRON, Postbus 2, 7990 AA Dwingeloo, Netherlands.
5 Department of Astrophysics, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL Nijmegen, Netherlands.
* To whom correspondence should be addressed. E-mail: brunthaler{at}jive.nl
