The XXL Survey: IV. Mass-temperature relation of the bright cluster sample

Context. The XXL Survey is the largest survey carried out by XMM-Newton. Covering an area of 50 deg², the survey contains ~450 galaxy clusters out to a redshift ~2 and to an X-ray flux limit of ~ 5 × 10^-15 erg s^-1 cm^-2. This paper is part of the first release of XXL results focussed on the bright cluster sample.

Aims. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation discussed in this article is used to estimate the mass of all 100 clusters in XXL-100-GC.

Methods. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS shear catalog, we derive the weak-lensing mass of each system with careful considerations of the systematics. The clusters lie at 0.1 <z< 0.6 and span a temperature range of T ≃ 1−5 keV. We combine our sample with an additional 58 clusters from the literature, increasing the range to T ≃ 1−10 keV. To date, this is the largest sample of clusters with weak-lensing mass measurements that has been used to study the mass-temperature relation.

Results. The mass-temperature relation fit (M ∝ T^b) to the XXL clusters returns a slope b = 1.78^+0.37_-0.32 and intrinsic scatter σ_lnM|T≃ 0.53; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, b = 1.67 ± 0.12 and σ_lnM|T ≃ 0.41.

Conclusions. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of ~1 keV temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.