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T. B. O'Hara, J. J. Mohr (University of illinois), J. J. Bialek, A. E. Evrard (University of Michigan)
A detailed understanding of galaxy cluster scaling relations will be necessary for surveys using clusters to study cosmology. In particular, there are open questions regarding the effects of merger activity and cooling processes on the evolution of scaling relations and the scatter of clusters about these relations. We present here results of a study of the relationship between scatter about cluster scaling relations and substructure and cool core properties in nearby galaxy clusters. Using a sample of 45 nearby galaxy clusters, we construct scaling relations between emission-weighted mean temperature and X-ray luminosity, intracluster medium (ICM) mass, isophotal size, and near-IR luminosity. We classify clusters as cool core (CC) or non-cool core (NCC) based on their central cooling time, and quantify ICM substructure via four different measures. We attempt to minimize cool core-related separation on scaling relations via a simple uniform temperature scaling of CC clusters, and by introducing central surface brightness as a third parameter in observable--temperature scaling relations.
We find that CC clusters and clusters with less substructure generally exhibit greater scatter about observable--temperature scaling relations. This holds true not only for observables that are highly sensitive to core structure (such as X-ray luminosity projected within r2500), but also for relations that are more sensitive to structure well outside the core (such as core-subtracted X-ray luminosity). This suggests that processes more global than core radiative instability are at work. Simulations without cooling mechanisms show roughly equal scatter in low- and high-substructure clusters. Our results appear not to support the scenario in which clusters evolve cool cores over time in the absence of major mergers.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.