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 .

We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect signature from 2500 deg 2 of South Pole Telescope (SPT) data. This work represents the complete sample of clusters detected at high significance in the 2500 deg 2 SPT-SZ survey, which was completed in 2011. A total of 677 (409) cluster candidates are identified above a signal-to-noise threshold of ξ = 4.5 (5.0). Ground-and space-based optical and near-infrared (NIR) imaging confirms overdensities of similarly colored galaxies in the direction of 516 (or 76%) of the ξ > 4.5 candidates and 387 (or 95%) of the ξ > 5 candidates; the measured purity is consistent with expectations from simulations. Of these confirmed clusters, 415 were first identified in SPT data, including 251 new discoveries reported in this work. We estimate photometric redshifts for all candidates with identified optical and/or NIR counterparts; we additionally report redshifts derived from spectroscopic observations for 141 of these systems. The mass threshold of the catalog is roughly independent of redshift above z ∼ 0.25 leading to a sample of massive clusters that extends to high redshift. The median mass of the sample is M 500c (ρ crit ) ∼ 3.5 × 10 14 M h −1 70 , the median redshift is z med = 0.55, and the highest-redshift systems are at z >1.4. The combination of large redshift extent, clean selection, and high typical mass makes this cluster sample of particular interest for cosmological analyses and studies of cluster formation and evolution.