HEAD Division Meeting 1999, April 1999
Session 4. Clusters of Galaxies
Poster, Monday, April 12, 1999, 8:30am-6:10pm, Gold Room

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[4.10] A Multiphase Model for the Intracluster Medium

D. Nagai (Physics Department, University of Michigan), M.E. Sulkanen (NASA-MSFC), A.E. Evrard (Physics Department, University of Michigan)

Constraints on the clustered mass density \Omegam of the universe derived from the observed population mean intracluster gas fraction \langle fICM \rangle of x-ray clusters may be biased by reliance on a single-phase assumption for the thermodynamic structure of the intracluster medium (ICM). We propose a descriptive model for multiphase structure in which a spherically symmetric ICM contains isobaric density perturbations with a radially dependent variance \sigma2(r) = \sigmac2 (1+r2/rc2)-\epsilon. The model extends the work of Gunn & Thomas (1996) which assumed constant (radially independent) density fluctuations thoughout the ICM.

Fixing the x-ray emission and emission weighted temperature, we explore two independently observable signatures of the model in the {\sigmac,\epsilon} space. For bremsstrahlung dominated emission, the central Sunyaev-Zel'dovich (SZ) decrement in the multiphase case is increased over the single-phase case and multiphase x-ray spectra in the range 0.1-20 keV are flatter in the continuum and exhibit stronger low energy emission lines than their single-phase counterpart. We quantify these effects for a fiducial 108 K cluster and demonstrate how the combination of SZ and x-ray spectroscopy can be used to identify a preferred location {\hat{\sigma}c,\hat{\epsilon}} in the model space. From these parameters, the correct value of \langle fICM \rangle in the multiphase model results, allowing an unbiased estimate of \Omegam to be recovered.

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