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The first building block for using galaxy clusters in astrophysics and cosmology is an accurate determination of their mass, which can be estimated with weak lensing (WL) determinations or X-ray analyses assuming hydrostatic equilibrium (HE). By comparing the two mass proxies in well observed samples of rich clusters, we determined the intrinsic scatters, σWL ∼15 per cent for WL masses and σHE ∼25 per cent for HE masses. The certain assessment of the bias is hampered by differences as large as ∼40 per cent in either WL or HE mass estimates reported by different groups. If the scatter in the mass proxy is not considered, the slope of any scaling relation ‘mass–observable ’ is biased towards shallower values, whereas the intrinsic scatter of the scaling is over-estimated.
Sereno et al. (Wed,) studied this question.