Abell 754: A Non–Head-on Collision of Subclusters

We have analyzed spatially resolved spectra of A754 obtained with ASCA. Thecombination of spectral and imaging capabilities of ASCA has set unprecedentedconstraints on the hydrodynamical effects of a cluster merger. We findsignificant gas temperature variations over the cluster face, indicating shockheating of the atmosphere during the merger. The hottest region, >12 keV, islocated in the region of the Northwest galaxy clump though the entire regionalong the cluster axis appears to be hotter than the mean cluster temperature(~9 keV). The cool, ~5 keV gas originally found with the HEAO1-A2 experiment,resides in the exterior of the cluster atmosphere and in plume of gas weidentify with a stripped cool atmosphere of the infalling subcluster. We havealso attempted to reconstruct an iron abundance map of this merging system.Though poorly constrained, no significant deviations of abundance from the meanvalue are apparent in the individual regions. A754 is the only cluster so far which shows the significant temperaturepattern expected in a subcluster merger, in both the ROSAT (Henry & Briel 1995)and ASCA data, providing the first possibility to compare it with theoreticalpredictions. The observed temperature and surface brightness maps suggest thatthe two colliding subunits have missed each other by about 1 Mpc, and are nowmoving perpendicular to the cluster axis in the image plane (as, e.g., in thesimulations by Evrard etal 1996).Comment: Latex, 10 pages, 3 figures incl. color plate, uses aaspp4.sty, flushrt.sty and pstricks.sty. Submitted to ApJ Letter