Cluster Cosmology

h1. Paper pool

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h2. The physics inside the scaling relations for X-ray galaxy clusters: gas clumpiness, gas mass fraction and slope of the pressure profile

S. Ettori (INAF-OA Bologna)

In galaxy clusters, the relations between observables in X-ray and millimeter wave bands and the total mass have normalizations, slopes and redshift evolutions that are simple to estimate in a self-similar scenario. We study these scaling relations and show that they can be efficiently expressed, in a more coherent picture, by fixing the normalizations and slopes to the self-similar predictions, and advocating, as responsible of the observed deviations, only three physical mass-dependent quantities: the gas clumpiness $C$, the gas mass fraction $f_g$ and the logarithmic slope of the thermal pressure profile $\beta_P$. We use samples of the observed gas masses, temperature, luminosities, and Compton parameters in local clusters to constrain normalization and mass dependence of these 3 physical quantities, and measure: $C^{0.5} f_g = 0.110 (\pm 0.002 \pm 0.002) \left( E_z M / 5 \times 10^{14} M_{\odot} \right)^{0.198 (\pm 0.025 \pm 0.04)}$ and $\beta_P = -d \ln P/d \ln r = 3.14 (\pm 0.04 \pm 0.02) \left( E_z M / 5 \times 10^{14} M_{\odot} \right)^{0.071 (\pm 0.012 \pm 0.004)}$, where both a statistical and systematic error (the latter mainly due to the cross-calibration uncertainties affecting the \cxo\ and \xmm\ results used in the present analysis) are quoted. The degeneracy between $C$ and $f_g$ is broken by using the estimates of the Compton parameters. Together with the self-similar predictions, these estimates on $C$, $f_g$ and $\beta_P$ define an inter-correlated internally-consistent set of scaling relations that reproduces the mass estimates with the lowest residuals. 

h2. CFHTLenS: Weak lensing calibrated scaling relations for low mass clusters of galaxies

K. Kettula, S. Giodini, E. van Uitert, H. Hoekstra, A. Finoguenov, M. Lerchster, T. Erben, C. Heymans, H. Hildebrandt, T. D. Kitching, A. Mahdavi, Y. Mellier, L. Miller, M. Mirkazemi, L. Van Waerbeke, J. Coupon, E. Egami, L. Fu, M. J. Hudson, J. P. Kneib, K. Kuijken, H. J. McCracken, M. J. Pereira, B. Rowe, T. Schrabback, M. Tanaka, M. Velander

We present weak lensing and X-ray analysis of 12 low mass clusters from the CFHTLenS and XMM-CFHTLS surveys. We combine these systems with high-mass systems from CCCP and low-mass systems from COSMOS to obtain a sample of 70 systems, which we divide into subsamples of 15 merging and 55 relaxed systems. We measure L-T, M-L and M-T scaling relations and find in all cases that the power-law slopes of the full, merging and relaxed subsamples are consistent. For the M-T we find slopes consistent with the self-similar model, whereas L-T results in steeper and M-L in flatter relations. We find a marginal trend for larger scatter and lower normalisation in the M-L and M-T relations for the merging subsample, which we attribute to triaxiality and substructure. We explore the effects of X-ray cross-calibration and find that Chandra calibration leads to flatter L-T and M-T relations. We also utilise the three surveys making up the sample as overlapping mass bins. For COSMOS and CFHTLS we find slopes consistent with the relation fitted to the full sample, whereas the high mass CCCP sample favours flatter slopes. We also find that intermediate mass systems have a higher mass for their luminosity. Unfortunately our sample does not enable direct measurement of a break at low masses, but we find a trend for enhanced intrinsic scatter in mass at low masses. 

h2. A Simple Physical Model for the Gas Distribution in Galaxy Clusters

Anna Patej, Abraham Loeb

The dominant baryonic component of galaxy clusters is hot gas whose distribution is commonly probed through X-ray emission arising from thermal bremsstrahlung. The density profile thus obtained has been traditionally modeled with a beta-profile, a simple function with only three parameters. However, this model is known to be insufficient for characterizing the range of cluster gas distributions, and attempts to rectify this shortcoming typically introduce additional parameters to increase the fitting flexibility. We use cosmological and physical considerations to obtain a family of profiles for the gas with fewer parameters than the beta-model but which better accounts for observed gas profiles over wide radial intervals.