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Session 102 - Clusters of Galaxies.
Display session, Thursday, January 16
We present velocites measured for galaxies in the cluster A2256 using the Hydra multi-object spectrograph on the WIYN telescope. ROSAT observations of the complex X-ray structure of this cluster suggest that it represents an ongoing merger of subclumps. The spectra cover the wavelength range 5000--10,000 ÅVelocities were determined by cross correlation. Due to the large number of sky lines in the red, only wavelengths shorter than 7500 Å\ were used in the cross correlations. The galaxy spectra were correlated against three template spectra, representing two K giants and one nearby galaxy. We obtained a total of 128 new radial velocities, as well as 35 remeasurements of galaxies that had previously been observed. When combined with the 90 previously determined radial velocites, the total radial velocity sample for A2256 contains 218 galaxies. We will perform a number of statistical tests on these radial velocities to assess the evidence for substructure in the velocity distribution. We will also correlate any velocity substructure found with spatial substructure, based on photometry of a 3\times3 mosaic of deep R-band CCD images that we obtained with the WIYN telescope. These data will be compared with the results of our program of N-body simulations of cluster mergers.
Program listing for Thursday