The Observational Consequences of Merging Clusters of Galaxies

We present an observational analysis of numerical simulations of galaxycluster mergers. We identify several observational signatures of recent mergeractivity, and quantitatively assess the uncertainty introduced into clustermass estimates when invoking the commonly held assumptions of hydrostaticequilibrium, virial equilibrium, spherical symmetry and isothermality. We findthat mergers result in multiple X-ray peaks, long-lived elongation of the X-rayemission as well as isophotal twisting and centroid shifting to a degreeconsistent with recent observations. We also find an enlargement of the X-raycore relative to the dark matter core. Mergers result in non-isothermalclusters exhibiting observable inhomogeneities in the emission-weighted X-raytemperature of several keV on linear scales of less than 0.5 Mpc. The resultinggas dynamics are extremely complex, and we present an example of what might beobserved by a high resolution X-ray spectrograph. We further speculate that thegas dynamics, via shocks, bulk flows and turbulence, play an important role inthe evolution of cluster galaxies and associated radio sources, particularlywide-angle tailed (WAT) sources and radio halos. We find that X-ray based bycluster mass estimates made under equilibrium assumptions can be uncertain 50\%or more in the first 2 Gyrs after a merger and by up to 25\% after 2 Gyrsdepending on the details of the analysis and projection effects. Uncertaintiescan be considerably larger if the temperature is not well constrained.Comment: 42 pages, Latex, 23 postscript figures, Accepted for publication in Ap