Abstract
We study the dynamical state and the integrated total mass profiles of 75 massive (M500 > 5 × 1014 M⊙) Sunyaev–Zeldovich(SZ)-selected clusters at 0.08 < z < 1.1. The sample is built from the Planck catalogue, with the addition of four SPT clusters at z > 0.9. Using XMM-Newton imaging observations, we characterise the dynamical state with the centroid shift ⟨w⟩, the concentration CSB, and their combination, M, which simultaneously probes the core and the large-scale gas morphology. Using spatially resolved spectroscopy and assuming hydrostatic equilibrium, we derive the total integrated mass profiles. The mass profile shape is quantified by the sparsity, that is the ratio of M500 to M2500, the masses at density contrasts of 500 and 2500, respectively. We study the correlations between the various parameters and their dependence on redshift. We confirm that SZ-selected samples, thought to most accurately reflect the underlying cluster population, are dominated by disturbed and non-cool core objects at all redshifts. There is no significant evolution or mass dependence of either the cool core fraction or the centroid shift parameter. The M parameter evolves slightly with z, having a correlation coefficient of ρ = −0.2 ± 0.1 and a null hypothesis p-value of 0.01. In the high-mass regime considered here, the sparsity evolves minimally with redshift, increasing by 10% between z < 0.2 and z > 0.55, an effect that is significant at less than 2σ. In contrast, the dependence of the sparsity on dynamical state is much stronger, increasing by a factor of ∼60% from the one third most relaxed to the one third most disturbed objects, an effect that is significant at more than 3σ. This is the first observational evidence that the shape of the integrated total mass profile in massive clusters is principally governed by the dynamical state and is only mildly dependent on redshift. We discuss the consequences for the comparison between observations and theoretical predictions.
Highlights
The shape of the dark matter profile in galaxy clusters is a sensitive test of the nature of dark matter and of the theoretical scenario of structure formation
Complementary techniques can measure the total mass density profile, for example, galaxy velocities; strong gravitational lensing in the centre and weak lensing at large scale; X-ray estimates using the intra-cluster medium (ICM) density and temperature profiles and the hydrostatic equilibrium (HE) equation
Our initial sample is built from the 28 clusters with spectroscopic 0.5 < z < 0.9 in the sample of the XMM-Newton Large Programme (LP) ID069366, consisting of clusters detected at high S /N with Planck, and confirmed by autumn 2011 to be at z > 0.5
Summary
The shape of the dark matter profile in galaxy clusters is a sensitive test of the nature of dark matter and of the theoretical scenario of structure formation. X-ray observations are an excellent tool with which to undertake such studies – the ICM morphology can be used to infer the dynamical state, while the total mass profile can be derived by applying the hydrostatic equilibrium (HE) equation to spatially resolved density and temperature profiles. While this method yields the highest statistical precision on individual profiles over a wide radial range and up to high z (Amodeo et al 2016; Bartalucci et al 2018), it has the drawback of a systematic uncertainty due to any departure of the gas from HE, which must be taken into account.
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