Abstract:
The unparalleled resolution and sensitivity of Advanced Camera for Surveys on HST enable unprecedentedly detailed mapping of dark matter in many interesting galaxy clusters. I will present our recent gravitational lensing analysis of three most intriguing galaxy clusters: MS1054-0321, CL0152-1357, and CL0024+17. Dark matter in MS1054-0321 and CL0152-1357 follows the clusters' optical light very closely, showing filamentary structures when the Universe is half its present age. Mass reconstruction in CL0024+17 reveals a striking ring-like dark matter substructure at 75" from the cluster center, which might indicate the previous high-speed line-of-sight collision 1~2 Gyrs ago. In many respects, the current specification of SNAP resembles that of HST/ACS except for its much larger field of view. Therefore, these exciting results obtained from ACS are precursors of numerous scientific breakthroughs that will be brought by SNAP.