TRACING THE PECULIAR DARK MATTER STRUCTURE IN THE GALAXY CLUSTER Cl 0024+17 WITH INTRACLUSTER STARS AND GAS

Intracluster light (ICL) is believed to originate from the stars stripped from cluster galaxies. They are no longer gravitationally bound to individual galaxies, but to the cluster, and their smooth distribution potentially makes them serve as much denser tracers of the cluster dark matter than the sparsely distributed cluster galaxies. We present our study of the ICL in the galaxy cluster Cl 0024+17 using both Advanced Camera for Surveys (ACS) and Subaru data, where we previously reported the discovery of a ring-like dark matter structure with gravitational lensing. The ACS images provide much lower sky levels than ground-based data, and enable us to measure relative variation of surface brightness reliably. This analysis is repeated with the Subaru images to examine if consistent features are recovered despite a different reduction scheme and different instrumental characteristics. We find that the ICL profile clearly resembles the peculiar mass profile, which stops decreasing at r similar to 50 '' (similar to 265 kpc) and slowly increases until it turns over at r similar to 75 '' (similar to 397 kpc). This feature is seen in both ACS and Subaru images for nearly all available passband images while the features are in general stronger in red filters. The consistency across different filters and instruments strongly rules out the possibility that the feature might come from any residual, uncorrected calibration errors. In addition, our re-analysis of the cluster X-ray data shows that the peculiar mass structure is also indicated by a non-negligible (3.7 sigma in Chandra and 2.4 sigma in XMM-Newton) bump in the intracluster gas profile when the geometric center of the dark matter ring, not the peak of the X-ray emission, is chosen as the center of the radial bin. The location of the gas ring is closer to the center by similar to 15 '' (similar to 80 kpc), raising an interesting possibility that the ring-like structure is expanding and the gas ring is lagging