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 8.2 m telescope and the Sunyaev-Zel'dovich Array. The M $_WL$-Y $_sph$ scaling relations, measured at $\Delta$ = 500, 1000, and 2500 $\rho$$_ 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. }