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 sub(WL), and integrated Compton parameter Y sub(sph). Observations of 18 galaxy clusters at z [Asymptotically = to] 0.2 were obtained with the Subaru 8.2 m telescope and the Sunyaev-Zel'dovich Array. The M sub(WL)-Y sub(sph) scaling relations, measured at Delta = 500, 1000, and 2500 [rho] sub(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 sub(WL) at fixed Y sub(sph) of 20%, larger than both previous measurements of M sub(HSE)-Y sub(sph) scatter as well as the scatter in true mass at fixed Y sub(sph) found in simulations. Moreover, the scatter in our lensing-based scaling relations is morphology dependent, with 30%-40% larger M sub(WL) for undisturbed compared to disturbed clusters at the same Y sub(sph) at r sub(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.