Anatomy of a Merger: A Numerical Model of A754

A754 is a well-observed cluster of galaxies which exhibits a variety ofmorphological peculiarities. These include a bar of X-ray emission that isoffset significantly from the galaxy distribution, an elongated X-ray surfacebrightness distribution extending between two distinct peaks in the galaxydistribution, and an extremely non-isothermal and asymmetric intraclustermedium (ICM) temperature morphology. Using these observational constraints, wepresent a numerical Hydro/N-body model of A754 in which two clusters (2.5:1mass ratio) have merged nearly in the plane of the sky less than 0.5 Gyrs agowith an impact parameter of ~120 kpc, and an impact velocity of ~2500 km/s(roughly the escape velocity of the primary cluster). Our models allow us toidentify the origin of A754's peculiar X-ray and temperature morphologies, theunderlying hydrodynamical processes that shape them, and their futureevolution. We make detailed predictions for future high resolution X-rayspectroscopic observations (e.g. ASTRO-E). We discuss general properties of ourmodels which will be characteristic of off-axis mergers. In particular, we findsignificant non-thermal pressure support within the central region which couldbias cluster mass estimates. We find significant angular momentum imparted onthe gas distribution in the cluster. We find that mixing of the subcluster gascomponents is an inefficient process, particularly at large radii. Finally, wefind that subsequent dark matter core passages result in an extended relaxationtimescale.Comment: 27 pages, including tables and figures. Latex, 10 postscript figures. Figures 2, 6, and 7 are color, but will also print as B/W. Accepted for publication in the Astrophysical Journa