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 _WL, and integrated Compton parameter Y _sph. 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 _WL-Y _sph scaling relations, measured at Δ = 500, 1000, and 2500 ρ_c, are consistent in slope and normalization with previous results derived under the assumption of hydrostatic equilibrium (HSE). We find an intrinsic scatter in M _WL at fixed Y _sph of 20%, larger than both previous measurements of M _HSE-Y _sph scatter as well as the scatter in true mass at fixed Y _sph found in simulations. Moreover, the scatter in our lensing-based scaling relations is morphology dependent, with 30%-40% larger M _WL for undisturbed compared to disturbed clusters at the same Y _sph at r ₅₀₀. 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.