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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.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.