Wednesday, July 17, 2013

Cosmography of the Local Universe

At Cosmography of the Local Universe there is a video showing the distribution and motion of the galaxies in our neighborhood. There is also an accompanying paper by Courtois, Pomar, Tully, Hoffman and Courtois. In the video "distances" are represented by velocities in km/s. It's difficult to figure out distances to galaxies directly, what we can actually measure is the "redshift" of spectral lines, which can be interpreted as a velocity, which is then assumed to also indicate distances, due to the fairly uniform expansion of our local universe. Another term appearing in the video is the 'Zone of Avoidance' or ZOA. Our own galaxy, the Milky Way, blocks our view of the galaxies, due to the the dust and stars of the Milky Way being concentrated around the plane of the Milky Way's disk. So we really don't have much information about the galaxies laying in those directions.
One of the characteristic features of the distribution of galaxies is the presence of voids: huge, roughly spherical regions in which galaxies are very sparse. I have a collection of interesting links to the literature about voids here.