1999/03/23 by Daisuke Nagai, D. Nagai, M. E. Sulkanen +1
Physics and Astronomy · #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2000.03484.x
published as Mon.Not.Roy.Astron.Soc. 316 (2000) 120 · Nine pages, submitted to Monthly Notices of the RAS. Seven postscript figures incoporated
arxiv created 1999/03/23 · openalex publication_date 2000/07/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
Constraints on the clustered mass density Ωm of the Universe derived from the observed population mean intracluster gas fraction 〈 fICM〉 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 The model extends the work of Gunn & Thomas, which assumed radially independent density fluctuations. The main limitation of the model is its lack of connection to ICM dynamics. Fixing the X-ray emission profile and emission-weighted temperature, we explore two independently observable signatures of the model in the σc,ε space. For bremsstrahlung-dominated emission, the central Sunyaev-Zeldovich (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 c, in the model plane. From these parameters, the correct value of 〈 fICM〉 in the multiphase model results, allowing an unbiased estimate of Ωm to be recovered. The degree of consistency of current determinations of the Hubble constant via SZ and X-ray observations with values determined by other methods implies that biases in ICM gas fractions are not large.