LoCuSS: The Sunyaev-Zel'dovich Effect and Weak-lensing Mass Scaling Relation

We present the first weak-lensing-based scaling relation between galaxy cluster mass, M , and integrated Compton parameter Y . Observations of 18 galaxy clusters at z ≃ 0.2 were obtained with the Subaru 8.2m telescope and the Sunyaev-Zel'dovich Array. The M -Y scaling relations, measured at Δ = 500, 1000, and 2500 ρ , are consistent in slope and normalization with previous results derived under the assumption of hydrostatic equilibrium (HSE). We find an intrinsic scatter in M at fixed Y of 20%, larger than both previous measurements of M -Y scatter as well as the scatter in true mass at fixed Y found in simulations. Moreover, the scatter in our lensing-based scaling relations is morphology dependent, with 30%-40% larger M for undisturbed compared to disturbed clusters at the same Y at r . Further examination suggests that the segregation may be explained by the inability of our spherical lens models to faithfully describe the three-dimensional structure of the clusters, in particular, the structure along the line of sight. We find that the ellipticity of the brightest cluster galaxy, a proxy for halo orientation, correlates well with the offset in mass from the mean scaling relation, which supports this picture. This provides empirical evidence that line-of-sight projection effects are an important systematic uncertainty in lensing-based scaling relations.