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Cluster Mass Function (cluster + mass_function)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Abundances, masses and weak-lensing mass profiles of galaxy clusters as a function of richness and luminosity in ,CDM cosmologies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2010
Stefan Hilbert
ABSTRACT We test the concordance , cold dark matter (,CDM) cosmology by comparing predictions for the mean properties of galaxy clusters to observations. We use high-resolution N -body simulations of cosmic structure formation and semi-analytic models of galaxy formation to compute the abundance, mean density profile and mass of galaxy clusters as a function of richness and luminosity, and we compare these predictions to observations of clusters in the Sloan Digital Sky Survey (SDSS) maxBCG catalogue. We discuss the scatter in the mass,richness relation, the reconstruction of the cluster mass function from the mass,richness relation and fits to the weak-lensing cluster mass profiles. The impact of cosmological parameters on the predictions is investigated by comparing results from galaxy models based on the Millennium Simulation (MS) and the WMAP1 simulation to those from the WMAP3 simulation. We find that the simulated weak-lensing mass profiles and the observed profiles of the SDSS maxBCG clusters agree well in shape and amplitude. The mass,richness relations in the simulations are close to the observed relation, with differences ,30 per cent. The MS and WMAP1 simulations yield cluster abundances similar to those observed, whereas abundances in the WMAP3 simulation are two to three times lower. The differences in cluster abundance, mass and density amplitude between the simulations and the observations can be attributed to differences in the underlying cosmological parameters, in particular the power spectrum normalization ,8. Better agreement between predictions and observations should be reached with a normalization 0.722 < ,8 < 0.9 (probably closer to the upper value), i.e. between the values underlying the two simulation sets. [source]

X-ray groups and clusters of galaxies in the Subaru,XMM Deep Field

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
A. Finoguenov
Abstract We present the results of a search for galaxy clusters in the Subaru,XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5,2 keV band of 2 × 10,15 erg cm,2 s,1 over one of the widest XMM,Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) , log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance ,8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed. [source]

The poorly constrained cluster disruption time-scale in the Large Magellanic Cloud

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
Geneviève Parmentier
ABSTRACT We use Monte Carlo simulations, combined with homogeneously determined age and mass distributions, based on multiwavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) star cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index ,=,2 assuming different cluster disruption time-scales. For each of these cluster disruption time-scales, we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a ,Poissonian',2 sense, model mass distributions and model two-dimensional distributions in log(mass) versus log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit (MlimV,,4.7 mag) above which the observed cluster sample is complete, one cannot constrain the characteristic cluster disruption time-scale for a 104 M, cluster, tdis4[where the disruption time-scale depends on cluster mass as tdis=tdis4(Mcl/104 M,),, with ,, 0.62], to better than a lower limit, tdis4, 1 Gyr. We conclude that the CFR has been increasing steadily from 0.3 clusters Myr,1 5 Gyr ago to a present rate of (20,30) clusters Myr,1 for clusters spanning a mass range of ,100,107 M,. For older ages, the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from ,1 cluster Gyr,1 15 Gyr ago to its present value. On the other hand, if the ICMF has always been a power law with a slope close to ,=,2, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution. [source]

Evolution of the cluster abundance in non-Gaussian models

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000
J. Robinson
We carry out N -body simulations of several non-Gaussian structure formation models, including Peebles' isocurvature cold dark matter model, cosmic string models, and a model with primordial voids. We compare the evolution of the cluster mass function in these simulations with that predicted by a modified version of the Press,Schechter formalism. We find that the Press,Schechter formula can accurately fit the cluster evolution over a wide range of redshifts for all of the models considered, with typical errors in the mass function of less than 25 per cent, considerably smaller than the amount by which predictions for different models may differ. This work demonstrates that the Press,Schechter formalism can be used to place strong model-independent constraints on non-Gaussianity in the Universe. [source]

Slicing cluster mass functions with a Bayesian razor

ASTRONOMISCHE NACHRICHTEN, Issue 8 2010
C.D. Sealfon
Abstract We apply a Bayesian "razor" to forecast Bayes factors between different parameterizations of the galaxy cluster mass function. To demonstrate this approach, we calculate the minimum size N-body simulation needed for strong evidence favoring a two-parameter mass function over one-parameter mass functions and visa versa, as a function of the minimum cluster mass (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]