Properties of the Intracluster Medium in an Ensemble of Nearby Galaxy Clusters

Abstract

We present a systematic analysis of the intracluster medium (ICM) in an X-ray flux limited sample of 45 galaxy clusters. Using archival ROSAT PSPC data and published ICM temperatures, we present best fit double and single β model profiles, and extract ICM central densities and radial distributions. We use the data and an ensemble of numerical cluster simulations to quantify sources of uncertainty for all reported parameters.We examine the ensemble properties within the context of models of structure formation and feedback from galactic winds. We present best fit ICM mass-temperature M ICM -T X relations for M ICM calculated within r 500 and 1h −1 50 Mpc. These relations exhibit small scatter (17%), providing evidence of regularity in large, X-ray flux limited cluster ensembles. Interestingly, the slope of the M ICM -T X relation (at limiting radius r 500 ) is steeper than the self-similar expectation by 4.3σ. We show that there is a mild dependence of ICM mass fraction f ICM on T X ; the clusters with ICM temperatures below 5 keV have a mean ICM mass fraction f ICM = 0.160 ± 0.008 which is significantly lower than that of the hotter clusters f ICM = 0.212 ± 0.006 (90% confidence intervals). In apparent contradiction with previously published analyses, our large, X-ray flux limited cluster sample provides no evidence for a more extended radial ICM distribution in low T X clusters down to the sample limit of 2.4 keV.By analysing simulated clusters we find that density variations enhance the cluster X-ray emission and cause M ICM and f ICM to be overestimated by ∼12%. Additionally, we use the simulations to estimate an f ICM depletion factor at r 500 . We use the bias corrected mean f ICM within the hotter cluster subsample as a lower limit on the cluster baryon fraction. In combination with nucleosynthesis constraints this measure provides a firm upper limit on the cosmological density parameter for clustered matter Ω M ≤ (0.36 ± 0.01)h −1/2 50 .

Magnetic turbulence in cool cores of galaxy clusters

“…We use the electron density, temperature and cool core radius reported in Mohr et al (1999). We measure the RM dispersion to be 1200 m −2 from the map published by Dreher et al (1987) after removing pixels from the map with extraordinary large RM jumps, which we associate with observational artefacts (nπ-ambiguities).…”

“…We use the electron density, temperature, cool core radius, and luminosity reported in Mohr et al (1999), and David et al (1993). To our knowledge, no RM measurements or magnetic £eld estimates are available for the centre of this and all following clusters.…”

Cosmological parameters

“…from the measurement of the deuterium abundance in highredshift Lyman limit systems, of which a third has recently been analyzed [66,122] and more are in the pipeline D. Tytler, these proceedings. Using X-ray data from an X-ray flux limited sample of clusters to estimate the baryon fraction f b = 0.075h −3/2 [84] gives Ω m = 0.25h −1/2 = 0.3 ± 0.1 using h = 0.65 ± 0.08. Estimating the baryon fraction using Sunyaev-Zel'dovich measurements of a sample of 18 clusters gives f b = 0.077h −1 [19], and implies Ω m = 0.25h −1 = 0.38 ± 0.1.…”

A Sunyaev-Zel’dovich Effect Survey for High Redshift Clusters

“…These mock SZE observations include noise and have exposures tuned so that we will be able to survey 1 deg 2 in a month. The N-body plus SPH simulations are state of the art simulations sampled from four different cosmological models: (1) SCDM: standard, biased Ω = 1 CDM, (2) OCDM: unbiased Ω m = 0.3 CDM, (3) LCDM: unbiased Ω m = 0.3 and Ω λ = 0.7 CDM, and (4) τ CDM: Ω m = 1 but CDM power spectrum with Γ = 0.24 (see [7,8] for more details). These simulations include only gas dynamics and gravity.…”