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Session 3 - Evolution of Galaxies & Clusters of Galaxies.
Display session, Monday, June 09
South Main Hall,
X-ray observations taken with ASCA, ROSAT, and HEAO1 are used to measure the magnetic field in the central region of five clusters of galaxies with diffuse radio halos. Lower limits in the range of \sim1 - 10 \muG are found which are higher than the typical field strength derived from Faraday rotation measurements for non-cooling flow clusters. The magnetic field would have to be more than 20-30 times higher to reconcile the mass determinations derived from X-ray observations with those from gravitational lensing. All five clusters show evidence of a recent major merger in their surface brightness distributions or temperture maps. The presence of a significant magnetic field may be linked to the merger process which acts to: strip interstellar magnetic fields from sub-cluster galaxies supplying a ''seed field" and (2) amplify the seed field through the dynamo effect which is driven by turbulent gas motions in the merging cluster atmospheres. Since the turbulent motion from sub-cluster merger only persists for \sim2 Gyr, strong magnetic fields are likely to be a transient phenomena which plays a significant role in the gas dynamics of merging and recent post-merger systems but not in the regular clusters used in mass measurements. This hypothesis for the origin of cluster magnetic fields may also account for the rarity of difuse radio halos.
Program listing for Monday