Sereno, MauroMauroSerenoETTORI, STEFANOSTEFANOETTORI2020-03-162020-03-1620150035-8711http://hdl.handle.net/20.500.12386/23296The authors thank Lauro Moscardini and Elena Rasia for useful discussions. MS acknowledges financial contributions from contracts ASI/INAF n.I/023/12/0 ‘Attività relative alla fase B2/C per la missione Euclid’, PRIN MIUR 2010-2011 ‘The dark Universe and the cosmic evolution of baryons: from current surveys to Euclid’, and PRIN INAF 2012 ‘The Universe in the box: multiscale simulations of cosmic structure’. SE acknowledges the financial contribution from contracts ASI-INAF I/009/10/0 and PRIN-INAF 2012 ‘A unique data set to address the most compelling open questions about X-Ray Galaxy Clusters’.The first building block to use galaxy clusters in astrophysics and cosmology is the accurate determination of their mass. Two of the most well-regarded direct mass estimators are based on weak lensing (WL) determinations or X-ray analyses assuming hydrostatic equilibrium (HE). By comparing these two mass measurements in samples of rich clusters, we determined the intrinsic scatters, σ<SUB>WL</SUB> ̃ 15 per cent for WL masses and σ<SUB>HE</SUB> ̃ 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 intrinsic scatter in the mass estimate is not considered, the slope of any scaling relation `observable-mass' is biased towards shallower values, whereas the intrinsic scatter of the scaling is overestimated.STAMPAenArticle10.1093/mnras/stv8102-s2.0-84938152904000360824000019https://academic.oup.com/mnras/article/450/4/3633/9904902015MNRAS.450.3633SFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation