Heating of the Intracluster Gas in the Triangulum Australis Cluster

Submitted to ApJ Letters, 1996 June 15 ASCA and ROSAT X-ray data are used to obtain a two-dimensional map of the gas temperature in the Triangulum Australis cluster of galaxies. We find that this hot (Te = 10.3 ± 0.8 keV) system displays a temperature peak (> 12 keV) at the cluster core and an asymmetric temperature decline with radius. The temperature rise toward the center approximately corresponds to the adiabatic relation. An underdense gas sector, which is found in the ROSAT cluster image eastward of the hot core, has a higher temperature than average at that radius (although with marginal significance). At this higher temperature, the gas pressure in this region is equal to that of the rest of the cluster at the same radius, but the specific entropy of this gas is significantly higher. We speculate that the existence of the central temperature peak and the displaced region of high-entropy gas indicates recent or ongoing heating of the intergalactic medium in this cluster. The high-entropy gas is probably expelled from the core where this heating occurs, expanding adiabatically to its present state. The most probable source of such heating is a subcluster merger, for which the hydrodynamic simulations predict a qualitatively similar temperature structure. Triangulum Australis is the second cluster (in addition to A754) in which ASCA has found a significant temperature nonuniformity resembling that expected in a subcluster merger.