The galaxy cluster CIZA J2242.8+5301 is a merging system with a prominent ( \raise 0.817 pt \hbox { $ \scriptstyle \sim$ } 2 Mpc long ) radio relic , which together with the morphology of the X-ray emission provides strong evidence for a violent collision along the north-south axis .
We present our constraints on the dark matter distribution of this unusual system using Subaru and Canada-France-Hawaii Telescope ( CFHT ) imaging data .
Measuring a high S/N lensing signal from this cluster is potentially a challenging task because of its proximity to the Milky Way plane ( \left|b \right| \sim 5 \arcdeg ) .
We overcome this challenge with careful observation planning and systematics control , which enables us to successfully map the dark matter distribution of the cluster with high fidelity .
The resulting mass map shows that the mass distribution of CIZA J2242.8+5301 is highly elongated along the north-south merger axis inferred from the orientation of the radio relics .
Based on our mass reconstruction , we identify two sub-clusters , which coincide with the cluster galaxy distributions .
We determine their masses using Markov-Chain-Monte-Carlo analysis by simultaneously fitting two Navarro-Frenk-White ( NFW ) halos without fixing their centroids .
The resulting masses of the northern and southern systems are M _ { 200 } = 11.0 _ { -3.2 } ^ { +3.7 } \times 10 ^ { 14 } M _ { \sun } and 9.8 _ { -2.5 } ^ { +3.8 } \times 10 ^ { 14 } M _ { \sun } , respectively , indicating that we are witnessing a post-collision of two giant systems of nearly equal mass .
When the mass and galaxy centroids are compared in detail , we detect \raise 0.817 pt \hbox { $ \scriptstyle \sim$ } 1 \arcmin ( \raise 0.817 pt \hbox { $ \scriptstyle \sim$ } 190 kpc ) offsets in both northern and southern sub-clusters .
After investigating the statistical significance of the offsets by bootstrapping both mass and galaxy centroids , we find that the galaxy luminosity-mass offset for the northern clump is statistically significant at the \gtrsim 2 \sigma level whereas the detection is only marginal for the southern sub-cluster in part because of a relatively large mass centroid error .
We conclude that it is yet premature to uniquely attribute the galaxy-mass misalignment to self-interaction of dark matter and discuss caveats .