.:Discussion:.

-Environmental Effects on SFR-

            Internally, meaning what characteristics of the galaxy itself can relate to SFR, morphology and color are the largest signifiers, where being bluer and a spiral type galaxy indicates a higher presence of star formation. Additionally, merging with another galaxy may in some cases produce violent starburst.

            Externally, meaning what characteristics of the cluster can affect galaxy SFR, density within the cluster and radius from the cluster center are most likely the cause of fluctuations in SFR, due to galaxy harassment and ram-pressure stripping.

-Evolution of SFR in Galaxy Clusters-

In previous studies there was a decrease in SFR from high redshift to low redshift clusters, and model of an aging universe was proposed wherein as the universe aged, less cool gas was available to form stars, and thus SFR decreases.

However, in my study of intermediate redshift clusters, I found that the average SFR is considerably higher than both high and low redshift clusters. I propose I new model of the evolution of star formation in the universe: at the beginning of the universe, galaxies and galaxy clusters were very disorganized and did not create new stars very quickly.  At the middle-aged universe (my study), galaxies and clusters were more organized and began to create stars much more quickly. Finally, at the present age of the universe, the cool gas in the galaxies was exhausted from the high star formation during the middle ages of the universe, and thus lower SFRs are found.

There was a peculiar finding with CL1227 though: it’s Sum SFR/M_cl was considerably lower than that of the other two mid z clusters; This might be due to two things:  while the other two clusters have very similar redshifts, CL1227’s redshift is the highest of them all, so perhaps there is a time in the universe where galaxies have violent bursts in star formation, or perhaps since CL1227 had no merging galaxies, their were no starburst galaxies present to add to the Sum SFR, as in the other clusters. The reason mergers may not be present is because although CL1227 is not as massive as CL1232, it is very massive yet has the least amount of star forming members, so it is less likely that merging and starburst would occur.

-Extensions-

One thing that could possibly be done for the environmental study is to eliminate AGN contribution. However, X-ray, radio, or IRAC data from the Spitzer Space Telescope is needed to identify AGN-containing galaxies, and even then only the AGN contribution can be identified, not quantified and removed. Doing this would only be useful for the environmental study, since the study of SFR over different redshifts was conducted with data from Finn et al, which also did not account for AGN.

            Also, since such a large spike in star formation in these three intermediate redshift clusters was found, more work needs to be conducted at mid-z to reach the same result with different clusters, and find out exactly why is spike is occurring.