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 \beta 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 } - \left < T _ { X } \right > relations for M _ { ICM } calculated within r _ { 500 } and 1 h ^ { -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 } - \left < T _ { X } \right > relation ( at limiting radius r _ { 500 } ) is steeper than the self-similar expectation by 4.3 \sigma .
We show that there is a mild dependence of ICM mass fraction f _ { ICM } on \left < T _ { X } \right > ; the clusters with ICM temperatures below 5 keV have a mean ICM mass fraction \left < f _ { ICM } \right > = 0.160 \pm 0.008 which is significantly lower than that of the hotter clusters \left < f _ { ICM } \right > = 0.212 \pm 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 \left < T _ { X } \right > 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 \sim 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 \Omega _ { M } \leq ( 0.36 \pm 0.01 ) h ^ { -1 / 2 } _ { 50 } .