Title: Dark Matter Substructures in Galaxy Clusters Revealed by Gravitational Lensing with Advanced Camera for Surveys


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.