Detailed Study of Systematics and Updated Weak Lensing Masses
MNRAS 449, 685–714 (2015) doi:10.1093/mnras/stv275
The Canadian Cluster Comparison Project: detailed study of systematics and updated weak lensing masses
Henk Hoekstra,1† Ricardo Herbonnet,1 Adam Muzzin,1 Arif Babul,2 Andi Mahdavi,3 Massimo Viola1 and Marcello Cacciato1 1Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands 2Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada 3Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA
Accepted 2015 February 8. Received 2015 February 6; in original form 2014 October 14
ABSTRACT Masses of clusters of galaxies from weak gravitational lensing analyses of ever larger samples are increasingly used as the reference to which baryonic scaling relations are compared. In this paper we revisit the analysis of a sample of 50 clusters studied as part of the Canadian Cluster Comparison Project. We examine the key sources of systematic error in cluster masses. We quantify the robustness of our shape measurements and calibrate our algorithm empirically using extensive image simulations. The source redshift distribution is revised using the latest state-of-the-art photometric redshift catalogues that include new deep near-infrared observa- tions. None the less we find that the uncertainty in the determination of photometric redshifts is the largest source of systematic error for our mass estimates. We use our updated masses to determine b, the bias in the hydrostatic mass, for the clusters detected by Planck. Our results suggest 1 − b = 0.76 ± 0.05 (stat) ± 0.06 (syst), which does not resolve the tension with the measurements from the primary cosmic microwave background. Key words: cosmology: observations – dark matter.
relations typically have intrinsic scatter that also needs to be mea- 1 INTRODUCTION sured, or at least accounted for. The observed number density of clusters of galaxies as a function of One way forward is to simulate the observable properties of mass and redshift depends sensitively on the expansion history of the clusters, but the complex non-linear physics involved limits the Universe and the initial conditions of the density fluctuations. Com- fidelity of such approaches, at least for the moment. Therefore parison with predictions from a model of structure formation can direct estimates of the clusters masses are needed. This can be thus constrain cosmological parameters, such as the mean density achieved through dynamical analyses, such as the measurement of m and the normalization of the matter power spectrum σ 8 (e.g. the motion of cluster members, or by measuring the temperature Bahcall & Fan 1998; Henry 2000; Reiprich & Bohringer¨ 2002; of the hot intracluster medium (ICM). However, in both cases the Henry et al. 2009), or the dark energy equation-of-state w (e.g. cluster is assumed to be in equilibrium, which is generally not a Vikhlinin et al. 2009; Mantz et al. 2010, 2015). For a recent review valid assumption. For instance, simulations suggest that hydrostatic see Allen, Evrard & Mantz (2011). X-ray masses are biased low (e.g. Rasia et al. 2006; Nagai, Vikhlinin The fact that the observations do not provide actual cluster counts &Kravtsov2007; Lau, Kravtsov & Nagai 2009). as a function of mass, but rather the number density of objects with A more direct probe of the (dark) matter distribution would be certain observational properties, such as the number of red galaxies preferable, which is provided by the gravitational lensing distor- or the X-ray flux within a given aperture, complicates a direct com- tion of background galaxies: the gravitational potential of the clus- parison with predictions: the cosmological interpretation requires ter perturbs the paths of photons emitted by these distant galax- knowledge of the selection function and the scaling relation be- ies, resulting in a slight, but measurable, coherent distortion. This tween the observable and the underlying mass. Furthermore, scaling in turn provides a direct measurement of the gravitational tidal field, which can be used to directly infer the projected mass dis- tribution. Note, however, that the comparison to baryonic trac- Based on observations from the Canada–France–Hawaii Telescope, which ers does typically depend on the assumed geometry of the clus- is operated by the National Research Council of Canada, le Centre National ter. For a recent review of the use of gravitational lensing to de la Recherche Scientifique and the University of Hawaii. study cluster masses and density profiles, we refer the reader to †E-mail: [email protected] Hoekstra et al. (2013).