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antoniseb
2005-Mar-04, 11:23 AM
Here's a New Scientist story about the use of Masers and the VLA to measure the proper motion of M33 [second nearest large galaxy] over several years.

Distant galaxy's subtle sidling measured (http://www.newscientist.com/article.ns?id=dn7095)

GOURDHEAD
2005-Mar-05, 02:13 PM
Good link, we don't hear much about proper motion of galaxies. This brings to mind a question about the proper motion component of cosmological expansion. When observing galaxies near 12 billion light years away, is the proper motion component measurable in as little as 20 or 30 years? I must say I have trouble visualizing what to expect; the baloon analogy is difficult to apply. Would cosmological expansion contribute to the magnitude of proper motion?

antoniseb
2005-Mar-05, 02:24 PM
Originally posted by GOURDHEAD@Mar 5 2005, 02:13 PM
Would cosmological expansion contribute to the magnitude of proper motion?
I'm guessing that cosmic expansion would make the angular proper motion of distant galaxies smaller, not larger, due to time-dilation effects and increased distance.

We haven't heard much about proper motions of galaxies in the past, because up till now, we've never measured one. It is an interesting side measurement in this story that they had to subtract off the parallax motion from the sun's motion around the Milky Way, and so they were able to also determine the parallax distance to M33 with fairly high precision [confirming the distances derived from secondary distance scales like Cepheids].

This appears to be another area that the SKA will be able to make some significant contributions to the mapping of the nearest 100 million lightyears.