Deep (103 ks) Chandra observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of M = 3.0 ± 0.6, propagating in front of a cold disrupted cloud. This makes Abell 665 the second cluster where a strong merger shock of M ≈ 3 has been detected, after the Bullet cluster. The shock velocity from jump conditions is consistent with (2.7 ± 0.7) × 10 3 km sec −1 . The new data also reveal a prominent southern cold front, with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.

We present a 66 ksec Chandra X-ray observation of the galaxy cluster RXJ0334.2-0111. This deep observation revealed a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and several intriguing substructures. The temperature across the bow shock jumps by a factor of ∼ 1.5 (from 4.1 keV to 6.2 keV), and is consistent with the Mach number M = 1.6 +0.5 −0.3 . A second inner surface brightness edge is a cold front that marks the border between infalling subcluster cool core and the ICM of the main cluster. The temperature across the cold front increases from 1.3 +0.3 −0.8 keV to 6.2 +0.6 −0.6 keV. We find an overpressurized region ∼ 250 kpc east of the cold front that is named "the eastern extension (EE)". The EE may be a part of the third subcluster in the ongoing merger. We also find a tail shaped feature that originates near the bow shock and may extend up to a distance of ∼ 1 Mpc. This feature is also likely overpressurized. The luminous FR-I radio galaxy, 3C89, appears to be the cD galaxy of the infalling subcluster. We estimated 3C89's jet power from jet bending and the possible interaction between the X-ray gas and the radio lobes. A comparison between the shock stand-off distance and the Mach number for all known shock front/cold front combinations suggests that the core is continuously shrinking in size by stripping.

We present the results of deep Chandra and XMM-Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic. The temperature and metallicity maps show clear evidence of a merger between the western subcluster and the primary cluster. We detect five X-ray surface brightness edges. Three of them near the cluster center are cold fronts (CFs): CF1 is associated with the infalling subcluster; CF2 is located in the east of the primary cluster and CF3 is to the west of the primary cluster core. The other two edges at cluster outskirts are shock fronts (SFs): SF1 near the radio relic in the NW has Mach numbers derived from the temperature and the density jumps respectively of MT = 1.62 ± 0.12 and Mρ = 1.23 ± 0.06; SF2 in the SE has MT = 1.54 ± 0.05 and Mρ = 1.16 ± 0.13. In the region of the radio relic there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse Compton emission, and therefore set a lower limit on the magnetic field (∼ 450 kpc from primary cluster center) of B > 1.0 μG for a single power-law electron spectrum or B > 0.4 μG for a broken power-law electron spectrum. We propose a merger scenario including a primary cluster, a subcluster, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.

The galaxy cluster system RXCJ0225.9-4154 with the two sub-clusters A3016 and A3017 is embedded in a large-scale structure filament with signatures of filamentary accretion. In a Chandra observation of this system at a redshift of z = 0.2195 we detect both clusters in X-rays. In addition we detect a filament of X-ray emission connecting the two clusters and a galaxy group therein. The main cluster, A3017, shows indications of shocks most probably from a recent interaction with cluster components along the filament axis as well as a cold front at about 150 kpc from the cluster centre. The filament between the two clusters is likely to be heated by the accretion shocks of the clusters. We discuss two scenarios for the origin of the X-ray filament between the two clusters. In the first scenario the material of the filament has been ripped off of A3017 during the fly-by of A3016 and is now trailing the latter sub-cluster. Support for this scenario is a gas deficit on the eastern side of A3017. In the second scenario the filament between the two clusters does not come from either of them, but a significant contribution could come from the galaxy group located inside and the entire structure is on its first collapse. We favour the second explanation as the gas mass in the filament seems to be too large to be supplied by the interaction of the two Abell clusters. The paper describes many properties of the components of this cluster merger system that are used to assist the interpretation of the observed configuration.

Recent advances in X-ray and microwave observations have provided unprecedented insights into the structure and evolution of the hot X-ray emitting plasma from their cores to the virialization region in outskirts of galaxy clusters. Recent Sunyaev-Zel'dovich (SZ) surveys (ACT, Planck, SPT) have provided new cluster catalogs, significantly expanding coverage of the mass-redshift plane, whileChandraandXMM-NewtonX-ray follow-up programs have improved our understanding of cluster physics and evolution as well as the surveys themselves. However, the current cluster-based cosmological constraints are still limited by uncertainties in cluster astrophysics. In order to exploit the statistical power of the current and upcoming X-ray and microwave cluster surveys, it is critical to improve our understanding of the structure and evolution of the hot X-ray emitting intracluster medium (ICM). In this session, we discussed recent advances in observations and simulations of galaxy clusters, with highlights on (i) the evolution of ICM profiles and scaling relations, (ii) physical processes operating in the outskirts of galaxy clusters, and (iii) impact of mergers on the ICM structure in groups and clusters.