Comparing Masses in Literature (CoMaLit)-I. Bias and scatter in weak lensing and X-ray mass estimates of clusters

Abstract

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, $\sigma_\mathrm{WL}\sim$15 per cent for WL masses and $\sigma_\mathrm{HE}\sim$25 per cent for HE masses. The certain assessment of the bias is hampered by differences as large as $\sim$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 over-estimated.Comment: 14 pages, 7 figures; v2: 16 pages, 8 figures, MNRAS in press; results unchanged; extended presentation of the statistical method and of the correlations; products from the CoMaLit series are hosted and updated at http://pico.bo.astro.it/~sereno/CoMaLi