Comparing different mass estimators for a large subsample of thePlanck-ESZ clusters

Abstract

Context. Total mass is arguably the most fundamental property for cosmological studies with galaxy clusters. The individual cluster masses can be obtained with different methods, each with its own biases and limitations. Systematic differences in mass measurements can strongly impact the determination of the hydrostatic bias and of the mass-observable relations, key requirements of many cluster abundance studies. Aims. We investigate the present differences in the mass estimates obtained through independent X-ray, weak-lensing, and dynamical studies using a large subsample of the Planck-ESZ clusters. We also discuss the implications for mass bias analyses. Methods. After assessing the systematic differences in the X-ray-derived masses reported by distinct groups, we examine the mass estimates obtained with independent methods and quantify the differences as the mean ratio 1-b = MHE/MWL, dyn, where HE refers to hydrostatic masses obtained from X-ray observations, WL refers to the results of weak-lensing measurements, and dyn refers to the mass estimates either from velocity dispersion or from the caustic technique. So defined, the 1-b parameter includes all possible astrophysical, observational, and methodological biases in one single value. Results. Recent X-ray masses reported by independent groups show average differences smaller than ∼10%, posing a strong limit on the systematics that can be ascribed to the differences in the X-ray analysis when studying the hydrostatic bias. The mean ratio between our X-ray masses and the weak-lensing masses in the LC2-single catalog is 1-b = 0.74 ± 0.06, which corresponds to a mass bias of 26 ± 6%, a value insufficient to reconcile the Planck cluster abundance and cosmic microwave background results. However, the mean mass ratios inferred from the WL masses of different projects vary by a large amount, with APEX-SZ showing a bias consistent with zero (1-b = 1.02 ± 0.12), LoCuSS and CCCP/MENeaCS showing a significant difference (1-b = 0.76 ± 0.09 and 1-b = 0.77 ± 0.10, respectively), and WtG pointing to the largest deviation (1-b = 0.61 ± 0.12), which would substantially reduce the tension between the Planck results. Because of small differences between our M − YX relation and the one used by the Planck collaboration, our X-ray masses are on average 7% lower (4% at the same physical radius) than the Planck masses and can further reduce the required bias. At odds with the WL results, the dynamical mass measurements show better agreement with the X-ray hydrostatic masses, although there are significant differences when relaxed or disturbed clusters are used. However, the comparison is currently limited by the small sample sizes. Conclisions. The systematic differences between total masses obtained with recent independent X-ray analyses are smaller than those found in previous studies. This shifts the focus to WL and dynamical studies for a better convergence of the level of mass bias. However, the ratios obtained using different mass estimators suggest that there are still systematics that are not accounted for in all the techniques used to recover cluster masses. This prevents the determination of firm constraints on the level of hydrostatic mass bias in galaxy clusters.

Timing the last major merger of galaxy clusters with large halo sparsity

“…Nevertheless, the caustic masses are known to be a biased estimator of HE ones at fixed Δ (see e.g. Sereno et al 2015;Maughan et al 2016;Ettori et al 2019;Lovisari et al 2020). Hence, it is important to test the results with sparsity estimates obtained using mass measured using with same technique.…”

The thermalisation of massive galaxy clusters

“…By crossmatching with LC 2 (Literature Catalogs of weak Lensing Clusters, Sereno 2015), which are standardised and homogenised compilations of clusters and groups with weak lensing mass estimates, we find weak lensing masses for 62 ESZ-XMM clusters 3 . By comparison, ESZ-XMM hydrostatic masses are found to be biased low by 26 ± 6 per cent (Lovisari et al 2020a). The analysis of the weak lensing subsample confirms the negative evolution of the 𝐸 th − 𝐸 𝜙 relation, 𝛾 = −0.1±0.9, but evidence is marginal since just 4 clusters at 𝑧 > 0.4 have known weak lensing mass.…”

Multi-probe analysis of the galaxy cluster CL J1226.9+3332: Hydrostatic mass and hydrostatic-to-lensing bias

“…Details on this analysis will be given in [28]. The hydrostaticto-lensing mass bias b HSE/lens = 1 − M HSE 500 /M lens 500 , can be an interesting indicator of effects coming from the non-thermal contributions to the pressure of the cluster and systematic effects in mass estimations [29,30]. Supposing that they are uncorrelated estimates, we have combined the probability distributions obtained for M HSE 500 and M lens 500 to get a distribution of the ratio, which can be translated into a probability distribution of the hydrostatic-to-lensing mass bias for CL J1226.9+3332.…”