The Coma Cluster

This morning,  (Sunday - I must admit to still being in bed when I pointed the distant telescope at my target), I used the T20 telescope in New Mexico to image some galaxies in the Coma Cluster. The target galaxy was NGC 4556 which is a small 13th magnitude elliptical galaxy in Coma with a major axis of 1.2 minutes of arc. Although this galaxy is not very exciting it sits between two "giants" in comparison - that I will come to shortly. 

This small section of my image shows NGC 4556.

I have named a few of the galaxies in this section of the image. This is a 300 second exposure using a 4 1/2 inch telescope yet galaxies down to 18th magnitude are visible in the image. 

For example the interesting little group of 14th and 15th magnitude  stars ( I have named this "The Hole Punch Asterism") at the top (North) of the image sits just above a galaxy PGC 4333526 which has a magnitude of 17.94. This is arrowed in the image on the left. This little galaxy has a major axis of around 24 seconds of arc and a minor axis of 12 seconds of arc. Not the easiest of targets! It is receding from us at a velocity of 38,665 km per second so assuming a value for Hubble's constant of 75km/second/Megaparsec this gives a distance of 516 Mparsecs or 1680 million light years. (Very approximately!!). This is too far to be a member of the Coma Cluster so is a background galaxy. It is a long way out bearing in mind the speed of light is 300,000 km/second. The "bright" galaxy at top left,IC 3560 or  PGC 3089322, has a magnitude of 16.39! It has a radial velocity of 7182 km/s giving it an approximate distance of 312 million light years on the same basis. This is about the distance accepted for the Coma Cluster so it is a cluster member!!

Less than one degree south of NGC 4556 on the same image there is the barred spiral galaxy NGC 4565 (below). This is also known as Caldwell C38 and was discovered by William Herschel. This is definitely one of my favourite galaxies. The galaxy to the lower right in this image is NGC 4562. Although C31 is in the constellation of Coma Berenices it is not part of the Coma Cluster and is less than one seventh of the distance to the cluster. NGC 4562 and NGC 4565 have similar radial velocities and are about the same distance away so NGC 4562 is much the smaller galaxy. 

Moving North from NGC 4556 by just over 1 degree finds another Caldwell object - Caldwell C36 or NGC 4559.