2004ApJ...604..604O

We present an analysis of a Chandra observation of the massive, nearby galaxy cluster A2319. A sharp surface brightness discontinuity–suggested by previous, lower angular resolution X-ray imaging–is clearly visible in the ACIS image. This ∼300 kpc feature suggests that a major merger is taking place with a significant velocity component perpendicular to the line of sight. The cluster emission-weighted mean temperature is 11.8±0.6 keV, somewhat higher than previous temperature measurements. The Chandra temperature map of A2319 reveals substructure resembling that anticipated based on hydrodynamic simulations of cluster mergers and shows an associated cool core not previously known. The map shows a separation between the intracluster medium (ICM) and galaxies of one subcluster, indicating a transient state in which the ICM has been stripped from the subcluster galaxies (and presumably the dark matter). Detailed analysis of the merger feature shows a pressure change across the surface brightness discontinuity by a factor of ≲2.5. The higher density side of the front has a lower temperature, suggesting the presence of a cold front similar to those in many other merging clusters. The velocity of the front is roughly sonic. We compare bulk properties of the ICM and galaxies in A2319 to the same properties in a large sample of clusters as a way of gauging the effects of the major merger. Interestingly, by comparing A2319 to a sample of 44 clusters studied with the ROSAT PSPC, we find that the X-ray luminosity, isophotal size, and ICM mass are consistent with the expected values for a cluster of its temperature; in addition, the K-band galaxy light is consistent with the light-temperature scaling relation derived from a sample of ∼100 clusters studied with the Two Micron All Sky Survey. Together, these results indicate either that the merger in A2319 has not been effective at altering the bulk properties of the cluster or that there are large but correlated displacements in luminosity, isophotal size, ICM mass, galaxy light, and emission-weighted mean temperature in this cluster.