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For refcode 1995ApJ...446..583B:
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1995ApJ...446..583B EVIDENCE FOR AN ON-GOING CLUSTER/GROUP MERGER IN ABELL 2255 JACK O. BURNS, KURT ROETTIGER, AND JASON PINKNEY Department of Astronomy, New Mexico State University, Las Cruces, NM 88003; jburns@nmsu.edu; kroettig@nmsu.edu;jpinkney@nmsu.edu RICK A. PERLE, AND FRAZER N. OWEN National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801; rperley@aoc.nrao.edu; lowen@aoc.nrao.edu AND WOLFGANG VOGES Max-Planck-Institut fur Extraterrestrische Physik, Postfach 1603, D- 85740, Garching bei Munchen, Germany; whv@mpe.dnet.nasa.gov Received 1994 July 20; accepted 1994 December 27 ABSTRACT We report on new X-ray, radio, and optical observations of the rich cluster Abell 2255. These new observations have revealed interesting and unusual characteristics at each wavelength band that are inconsistent with a simple, relaxed cluster. ROSAT all-sky survey (RASS) and CCD r- band images show that the cluster X-ray centroid does not coincide with any bright cluster galaxies or subgroup of galaxies. Furthermore, RASS spectra indicate cool (2 keV) gas within 5' of the X-ray centroid whereas Einstein MPC spectra indicate a temperature of 7.3 keV for the cluster as a whole. At 1240 km s^-1^, A2255 has one of the highest known Abell cluster velocity dispersions; also, the two brightest cluster galaxies are separated by an unusually large 2635 km s^-1^. Our new VLA 20 cm imaging has revealed a distorted, off-center, steep-spectrum diffuse radio source, previously labeled a radio halo, and a peculiar ridge of radio emission ~0.6 Mpc north of the X-ray centroid. We believe that these cluster properties can be understood if A2255 is in the process of merging with a galaxy group. We present a numerical Hydro/N-body simulation of such a merger which nicely reproduces the X-ray and galaxy velocity properties, and the merger has sufficient energy to power the diffuse cluster radio emission. Subject headings: galaxies: clusters: individual (A2255) - galaxies: interactions - intergalactic medium - radio continuum: galaxies - X-rays: galaxies
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