The XXL Survey

Abstract

Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction Ω b /Ω m . We make use of the sample of the 100 brightest galaxy clusters discovered in the XXL Survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. Since it spans a wide range of mass (10 13 −10 15 M ) and redshift (0.05−1.1) and benefits from a large set of multiwavelength data, the XXL-100-GC sample is ideal for measuring the global baryon budget of massive halos. We measure the gas masses of the detected halos and use a mass-temperature relation directly calibrated using weak-lensing measurements for a subset of XXL clusters to estimate the halo mass. We find that the weak-lensing calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found in previous studies using hydrostatic masses. Our best-fit relation between gas fraction and mass reads f gas,500 = 0.055 +0.007 −0.006 M 500 /10 14 M 0.21 +0.11 −0.10 . The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at r 500,MT . Our measurements require a hydrostatic bias 1 − b = M X /M WL = 0.72 +0.08 −0.07 to match the gas fraction obtained using lensing and hydrostatic equilibrium, which holds independently of the instrument considered. Comparing our gas fraction measurements with the expectations from numerical simulations, we find that our results favour an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed halos, which might suggest that weak-lensing masses are overestimated. In light of these results, we note that a mass bias 1 − b = 0.58 as required to reconcile Planck cosmic microwave background and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to our current understanding of galaxy clusters.

Multiwavelength study of X-ray luminous clusters in the Hyper Suprime-Cam Subaru Strategic Program S16A field

“…We find that our measurement Mgas = 5.10 70 M⊙ within the same radius is in good agreement with Eckert et al (2016 …”

“…The cluster is referred to as XXL091 in the XXL survey (Eckert et al 2016), and has Mgas = 5.00 is derived from a scaling relation between WL mass and X-ray temperature (Lieu et al 2016). We find that our measurement Mgas = 5.10 70 M⊙ within the same radius is in good agreement with Eckert et al (2016 …”

“…masses, f b = 0.146 ± 0.012, accounts for ∼ 80 − 90% of the cosmic mean baryon fraction. In comparison with gas and baryon fractions from the literature based on various mass measurements (Vikhlinin et al 2009a;Martino et al 2014;Mahdavi et al 2013;Okabe et al 2014b;Sun et al 2009;Eckert et al 2016;Giodini et al 2009;Chiu et al 2016), our measurements are somewhat higher than previous studies but overall are agreed. Differences of gas and baryon fractions between these studies are ∼ 8% and ∼ 7% at M500 ∼ 2.4 × 10 14 h −1 70 M⊙, respectively.…”

The XMM Cluster Outskirts Project (X-COP): Physical conditions of Abell 2142 up to the virial radius

“…For the deprojection, we compared the output of two different methods: the multiscale method described in Eckert et al (2015b) and an onion-peeling method (Ettori et al 2010). Both methods assume spherical symmetry.…”

“…Each component can then be easily deprojected to reconstruct the 3D profile. Following Eckert et al (2015b), we decompose the projected profile into a sum of King profiles, with s the projected radius, related to the line-of-sight distance and the 3D radius r, by:…”