X-ray and radio observations of CIZA J2242.8+5301 suggest that it is a major cluster merger .
Despite being well studied in the X-ray , and radio , little has been presented on the cluster structure and dynamics inferred from its galaxy population .
We carried out a deep ( i < 25 ) broad band imaging survey of the system with Subaru SuprimeCam ( g & i bands ) and the Canada France Hawaii Telescope ( r band ) as well as a comprehensive spectroscopic survey of the cluster area ( 505 redshifts ) using Keck DEIMOS .
We use this data to perform a comprehensive galaxy/redshift analysis of the system , which is the first step to a proper understanding the geometry and dynamics of the merger , as well as using the merger to constrain self-interacting dark matter .
We find that the system is dominated by two subclusters of comparable richness with a projected separation of 6.9 \arcmin ^ { +0.7 } _ { -0.5 } ( 1.3 ^ { +0.13 } _ { -0.10 } Mpc ) .
We find that the north and south subclusters have similar redshifts of z \approx 0.188 with a relative line-of-sight velocity difference of 69 \pm 190 \mathrm { km } \mathrm { s } ^ { -1 } .
We also find that north and south subclusters have velocity dispersions of 1160 ^ { +100 } _ { -90 } \mathrm { km } \mathrm { s } ^ { -1 } and 1080 ^ { +100 } _ { -70 } \mathrm { km } \mathrm { s } ^ { -1 } , respectively .
These correspond to masses of 16.1 ^ { +4.6 } _ { -3.3 } \times 10 ^ { 14 } M _ { \sun } and 13.0 ^ { +4.0 } _ { -2.5 } \times 10 ^ { 14 } M _ { \sun } , respectively .
While velocity dispersion measurements of merging clusters can be biased we believe the bias in this system to be minor due to the large projected separation and nearly plane-of-sky merger configuration .
CIZA J2242.8+5301 is a relatively clean dissociative cluster merger with near 1:1 mass ratio , which makes it an ideal merger for studying merger associated physical phenomena .