Scaling relations for galaxy clusters in the Millennium-XXL simulation

Abstract

We present a very large high-resolution cosmological N-body simulation, the Millennium-XXL or MXXL, which uses 303 billion particles to represent the formation of dark matter structures throughout a 4.1Gpc box in a LambdaCDM cosmology. We create sky maps and identify large samples of galaxy clusters using surrogates for four different observables: richness estimated from galaxy surveys, X-ray luminosity, integrated Sunyaev-Zeldovich signal, and lensing mass. The unprecedented combination of volume and resolution allows us to explore in detail how these observables scale with each other and with cluster mass. The scatter correlates between different mass-observable relations because of common sensitivities to the internal structure, orientation and environment of clusters, as well as to line-of-sight superposition of uncorrelated structure. We show that this can account for the apparent discrepancies uncovered recently between the mean thermal SZ signals measured for optically and X-ray selected clusters by stacking data from the Planck satellite. Related systematics can also affect inferences from extreme clusters detected at high redshift. Our results illustrate that cosmological conclusions from galaxy cluster surveys depend critically on proper modelling, not only of the relevant physics, but also of the full distribution of the observables and of the selection biases induced by cluster identification procedures.Comment: 19 pages, 12 figures. Replaced with version published in MNRA

Observational probes of cosmic acceleration

“…However, the results from the Planck Collaboration et al (2011b) have sounded a cautionary note, as the optical mass estimates used to derive cosmological parameters in Rozo et al (2010) appear to be inconsistent with SZ data (see also Draper et al, 2012). Biesiadzinski et al (2012) have attributed this inconsistency to miscentering, while Angulo et al (2012) point out the importance of systematics covariance. Rozo et al (2012c,b,a) argue that the optical, X-ray, and SZ data can be reconciled by considering, in addition to these effects, the systematics of X-ray temperature measurements indicated by the offsets among estimates from different groups, and departures from hydrostatic equilibrium at the level predicted by hydrodynamic cosmological simulations (e.g., Nagai et al 2007).…”

The abundance and colours of galaxies in high-redshift clusters in the cold dark matter cosmology

“…However, X-ray mass estimates are also uncertain due to the limitations in our understanding of the conditions in X-ray gas (e.g. Angulo et al 2012). Examples of intrinsic spectra for two synthetic galaxies at redshift z = 1.4, over-plotted with transmission profiles for the i, z, J and H bands, as shown by the shaded regions.…”

Scaling Relations for Galaxy Clusters: Properties and Evolution

“…Nagai et al 2007;Mahdavi et al 2008Mahdavi et al , 2012, although the required level of bias would be much larger than is expected from simulations and observations. Angulo et al (2012) used simulated clusters from the new Millennium-XXL simulations to show that the discrepancy in the amplitude can result from the Malmquist bias in flux limited samples. In this case the discrepancy would arise from the propagation of the Malmquist bias from the X-ray luminosities to the SZ signal through covariance in their scatter at fixed cluster mass (Fig.…”