An important compilation of galaxies in the Virgo cluster was presented by
Binggeli, Sandage and Tammann
1986, Astron. J. 90, 1681. Their Virgo Cluster Catalog consists of 2096 galaxies which they believed,
based on examination of high quality photographic plates, are likely cluster members.
Note that their investigation of the cluster
was based on many fewer redshifts than are available today.
To the right is the sky distribution of possible cluster
members as appeared in their paper. (If you click on the image, a larger
version will be displayed.)
Using the Virgo AGC/α.40 data files (linked above), plot (on the same graph)
the sky distribution of galaxies in the (a)
optical sample and (b) the α.40 galaxies.
Be sure to plot the distribution so that east is to the left and west is the right; why do we do that?
Consider the result: what do you notice and how can you explain what you see? How does your diagram
compare to that seen in Fig 2. of Binggeli+ (1986)?
Clusters of galaxies have a typical radius of 2 Mpc. At the distance of 16.7 Mpc, what
is the angular extent of 2 Mpc?