AAS 207th Meeting, 8-12 January 2006
Session 177 Galaxy Clusters across the Spectrum
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

[177.03] The Nature of the Velocity Gradient in Abell 576

R. Dupke, N. Mirabal, J. Bregman (University of Michigan)

We show here the results of an analysis of Chandra and XMM observations of Abell 576. We confirmed the detection of a significant velocity gradient along the NW(W)-E direction, in agreement with previous ASCA SIS measurements. The error weighted average over ACIS-S3, MOS1 & MOS2 for the maximum velocity difference is >3.3E+03km/s at the 90% confidence level, similar to the velocity limits estimated indirectly for bullet'' cluster (1E0657-56). This suggests that a supersonic merger with high line of sight component is currently being observed in Abell 576. The probability that the velocity gradient is generated by chance is <0.1% and it is still <1% for a 1-\sigma gain fluctuation of 103 km/s. We mapped the distribution of elemental abundance ratios across the cluster and we detected a strong E-W chemical discontinuity using the abundance ratio of Silicon to Iron, implying a clear separation between SN Ia and SN II ejecta dominance, varying from 100% SN Ia iron mass fraction in the West-Northwest to 32% in the East. This difference between metal enrichment histories further supports a merging scenario. The center of the cluster is located at the chemical discontinuity boundary. We argue for a model where a near line-of-sight merger is responsible for the X-ray derived physical characteristics of the cluster.