Homework Questions

Use Partiview to answer these questions:

1. What is the distance out to which the Tully Nearby Galaxies Catalog includes galaxies? Use the center click function to find the (x,y,z) coordinates of selected galaxies at the limit, and then calculate the distance from
   
   $$r=\sqrt{x^2+y^2+z^2}$$
   
   
   What is the lookback time corresponding to this distance? What would be the redshift if the Hubble Constant is 72 km/s mpc?
2. Orbit around the Tully galaxy distribution. Look for what seems to be a missing strip cut on a great circle right through the center. Line up on this cut, and then move all the way back in to the Milky Way. How does the plane of the Milky Way compare to this strip with no galaxies? Why would this happen in an optical catalog of galaxies?
3. Move back out again. Issue the command ``censize 15000000'' to increase the reference coordinates to 15 Mpc. The Virgo cluster is a little farther than this. Explore the data to identify clusters of galaxies not far from the North Galactic pole (the blue axis). One of these is the Virgo cluster. The catalog assigns nearly the same distance to all members of the cluster, so they show up as a flat patch of galaxies, while in reality they would be spread over different distances from us. You can identify each galaxy either by its label (which appears when it is close enough), or by a center click on the galaxy which then causes its coordinates and name to appear in the control panel window. There is a text version of the Tully Catalog of Nearby Galaxies on the computer system in /home/data/tully_galaxies/catalog.txt. You may scroll through the list using less catalog.txt . The entries include Right Ascension, Declination, V, and R. With some help from XEphem you can find which part of the sky these would appear in, and probably even find the galaxy as it shows in our sky. Where in the sky is the other cluster similar in size and distance to Virgo?

   Figure: Coordinate axes and the region around the Virgo Cluster.

   
4. How many galaxies are in the Virgo cluster and the other one noted above? Compare these clusters to the Local Group. From the coordinates of selected galaxies in these clusters measure the linear extent of these clusters perpendicular to the line of sight to them. Compare both the number of galaxies, and the size of the space these clusters occupy to one another, and to the local group. Is it reasonable to assume that these clusters are not gravitationally bound to the Local Group?
5. Use the data in catalog.txt to plot a Hubble law diagram for the Tully catalog. The last two columns of the data file are V and R. What is a best linear fit for the Hubble constant to these data?