.:Observations and Data Reduction:.

-Selection of Cluster Candidates-

Three clusters of similar intermediate range redshift (.5414 < z < .6355) yet inherently different physical properties were selected based upon their differences in mass, degree of relaxation, and virial radius (also R200), which is the radius at which the mean density of the cluster is 200 times the critical density of the universe, meaning that the galaxies will be able to resist universal expansion and separation from the cluster. Since R200 needs to be a certain radius to contain the galaxies, it is proportional to the mass of the cluster.

CL 1037.9-1243

This cluster is the least massive of the three clusters, with a virial radius of .57 mega parsecs (Mpc) and the lowest velocity dispersion (the faster the galaxies are moving, the more massive the cluster must be in order to retain them, so therefore velocity dispersion is proportional to the cube root of the mass of the cluster, as well as directly proportional to the virial radius[1]. There are 206 star forming galaxies in the 24 micron field, but only 45 of them are identified as members of the cluster, determined by their spectroscopic and photometric membership flags, making this cluster the second least populated. This cluster is also the least “relaxed” due to its cigar-like shape, meaning that its galaxies have not yet entered equilibrium. This also means that the velocity dispersions are not quite as accurate in determining the mass of the cluster, since the velocities could be those of when the galaxies entered the cluster, not yet retaining a uniform velocity.

CL 1227.9-1138         

This cluster is the middle of the road candidate, with the medium mass, velocity dispersion, and virial radius of 1.00 Mpc. The MIPS image has 145 galaxies present, but only 26 of those are cluster members, making it less populated with star forming galaxies than CL1037, and yet more massive and spread out. This cluster is also in the middle state of relaxation. Its galaxies are traveling less erratically than those of CL1037, but faster. Since the galaxies are moving considerably faster than those of CL1037, it is true that CL1227 is much more massive, since it needs to be so to retain its galaxies. However, it is not nearly as “relaxed” or massive as CL1232.

CL 1232.5-1250

This cluster is by far the most massive of the three and has the highest velocity dispersion and virial radius (1.99 Mpc, twice that of CL1227). It is by far the most populated with 162 MIPS galaxies in the image, 54 of those being identified as cluster members. This cluster is also the most “relaxed”, with the most uniform shape, but its galaxies have the highest velocity dispersion, and therefore this cluster is the most massive of all three.