THE OBSERVATIONAL CONSEQUENCES OF MERGING CLUSTERS OF GALAXIES

We present an observational analysis of the numerical simulations of g alaxy custer mergers. We identify several observational signatures of recent merger activity and quantitatively assess the uncertainty intro duced into cluster mass estimates when invoking the commonly held assu mptions of hydrostatic equilibrium, virial equilibrium, spherical symm etry, and isothermality. We find that mergers result in multiple X-ray peaks, long-lived elongation of the X-ray emission, as well as isopho tal twisting and centroid shifting to a degree consistent with recent observations. We also find an enlargement of the X-ray core relative t o the dark matter core. Mergers result in nonisothermal clusters exhib iting observable inhomogeneities in the emission-weighted X-ray temper ature of several keV on linear scales of less than 0.5 Mpc. The result ing gasdynamics are extremely complex, and we present an example of wh at might be observed by a high resolution X-ray spectograph We further speculate that the gas dynamics, via shocks, bulk flows, and turbulen ce, play an important role in the evolution of cluster galaxies and as sociated radio sources; particularly wide-angle tailed (WAT) sources a nd radio halos. We find that X-ray based cluster mass estimates made u nder equilibrium assumptions can be uncertain by 50% or more in the fi rst 2 Gyrs after a merger and by up to 25% after 2 Gyrs depending on t he details of the analysis and projection effects. Uncertainties can b e considerably larger if the temperature is not well constrained. Simi lar uncertainties are observed in the X-ray derived baryon mass fracti ons. Virial mass estimates are typically overestimated because the obs erved one-dimensional velocity dispersion can be severely contaminated by the infall velocity of the subcluster.