Spectroscopy of the hot intracluster medium has proven very revealing of its likely history

Spectroscopy of the hot intracluster medium has proven very revealing of its likely history

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Spectroscopy of the hot intracluster medium has proven very revealing of its likely history. By the advent of ASCA, X-ray features from specific ions could be resolved, so it was possible to examine the relative abundances of heavy elements to tell where they came from. In particular, the contributions of different kinds of supernovae (from different progenitor mass ranges) could tell what the early star-forming history of the cluster galaxies was like, and the abundance structure could tell whether virial motions or the energy input from galactic winds is more important. As an example, here are ASCA spectra of the inner and outer regions of Abell 496, from Dupke and White 2000 (ApJ 537, 123, by permission of the AAS). This plot shows clearly the reduced metallicity in the outer regions. Comparison of the abundances of these elements (Fe, Ni, Si, S, Mg) suggests that type II SN contributed everywhere, with type Ia most important in the inner parts of clusters (a sensible thing if much of
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Unformatted text preview: the mixing happened early on, since type IIs would have gone off before type Ia's). There is some evidence that significant heating can occur from supernova-driven winds, on top of the virial heating simply from being in equilibrium in the cluster potential. It was believed for some time, from the Einstein serendipity survey, that the X-ray luminosity function of clusters showed string evolution from about z =0.5 to the present in the direction of clusters brightening over time, but more complete ROSAT data call this into question and suggest that cluster X-ray properties have been nearly constant since z =0.7 (the WARPS survey - Fairley et al. 2000 MNRAS 315, 669; and Schindler 1999 A&A 349, 435). Out to redshifts of order 1, X-ray emission is the best way to identify rich groupings of galaxies, since detection of diffuse emission is less subject to projection biases than enhancements in projected galaxy density....
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