We present an observational analysis of numerical simulations of galaxy
cluster mergers. We identify several observational signatures of recent merger
activity, and quantitatively assess the uncertainty introduced into cluster
mass estimates when invoking the commonly held assumptions of hydrostatic
equilibrium, virial equilibrium, spherical symmetry and isothermality. We find
that mergers result in multiple X-ray peaks, long-lived elongation of the X-ray
emission as well as isophotal twisting and centroid shifting to a degree
consistent with recent observations. We also find an enlargement of the X-ray
core relative to the dark matter core. Mergers result in non-isothermal
clusters exhibiting observable inhomogeneities in the emission-weighted X-ray
temperature of several keV on linear scales of less than 0.5 Mpc. The resulting
gas dynamics are extremely complex, and we present an example of what might be
observed by a high resolution X-ray spectrograph. We further speculate that the
gas dynamics, via shocks, bulk flows and turbulence, play an important role in
the evolution of cluster galaxies and associated radio sources, particularly
wide-angle tailed (WAT) sources and radio halos. We find that X-ray based by
cluster 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 Gyrs
depending on the details of the analysis and projection effects. Uncertainties
can be considerably larger if the temperature is not well constrained.Comment: 42 pages, Latex, 23 postscript figures, Accepted for publication in
Ap
We investigate the predicted present-day temperature profiles of the hot,
X-ray emitting gas in galaxy clusters for two cosmological models - a current
best-guess LCDM model and standard cold dark matter (SCDM). Our
numerically-simulated "catalogs" of clusters are derived from high-resolution
(15/h kpc) simulations which make use of a sophisticated, Eulerian-based,
Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which
are essential for correctly modelling cluster temperatures. We show that the
temperature structure on Mpc-scales is highly complex and non-isothermal.
However, the temperature profiles of the simulated LCDM and SCDM clusters are
remarkably similar and drop-off as $T +AFw-propto (1+-r/a_x)^{-+AFw-delta}$
where $a_x +AFw-sim r_{vir}/1.5$ and $+AFw-delta +AFw-sim 1.6$. This decrease
is in good agreement with the observational results of Markevitch et al.(1998)
but diverges, primarily in the innermost regions, from their fit which assumes
a polytropic equation of state. Our result is also in good agreement with a
recent sample of clusters observed by BeppoSAX though there is some indication
of missing physics at small radii ($r<0.2 r_{vir}$). We discuss the
interpretation of our results and make predictions for new x-ray observations
that will extend to larger radii than previously possible. Finally, we show
that, for $r>0.2 r_{vir}$, our universal temperature profile is consistent with
our most recent simulations which include both radiative cooling and supernovae
feedback.Comment: 8 pages, 6 figures, accepted for publication in ApJ, full-page
version of Fig. 2 at
http://www.cita.utoronto.ca/+AH4-cloken/PAPERS/UTP/f2.ep
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