LoCuSS: THE SUNYAEV–ZEL'DOVICH EFFECT AND WEAK-LENSING MASS SCALING RELATION

Abstract

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 ∆ = 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.

Planckintermediate results

“…The scatter we observe (σ Y|M ∼ 20 percent) is also in excellent agreement with that seen by Marrone et al (2012). Although numerical simulations predict that there is intrinsically only of order ten percent scatter between the mass and the integrated Compton parameter (e.g., da Silva et al 2004), observational measurement uncertainties and complications due to, e.g., mass along the line of sight or cluster triaxiality introduce a further source of scatter.…”

“…A comparison to the most recent results of Marrone et al (2012), who also use weak lensing masses shows that, while the normalisations are in agreement, the slopes are slightly (although not significantly) shallower. This is easily explained by our exclusion of A383 from the regression analysis (see Sect.…”

“…The other, A383, while not obviously contaminated by a radio source and appearing to be a very relaxed system in X-rays, exhibits an offset exceeding 4 arcmin (∼0.8 R 500 ) between the SZ and X-ray positions. This cluster is detected at a rather low signal-to-noise ratio, and we also note that Marrone et al (2012), in their Sunyaev-Zeldovich Array (SZA) observations, found that this system has an unusually low SZ flux for its apparent mass. In addition, Zitrin et al (2012) find that A383 is a cluster-cluster lens system, where the nearby z = 0.19 cluster is lensing a more distant z = 0.9 object that lies about 4 to the north-east from the centre of the main system.…”

“…The only investigations of the mass-Y SZ relation using weak lensing masses published to date have been those of Marrone et al (2009Marrone et al ( , 2012, using data from the Local Cluster Substructure Survey (LoCuSS) 1 . The first directly compared 2D quantites (i.e., cylindrical SZ effect vs. projected mass) within a fixed physical radius of 350 kpc, while the second compared the spherically integrated Compton parameter against deprojected mass.…”

“…In all panels the dark grey region represents the best-fitting relation obtained with slope and normalisation as free parameters, and the light grey region denotes the best-fitting relation obtained with the slope fixed to the self-similar value of 5/3. Previous results from Marrone et al (2012), Bonamente et al (2008), and the analysis of 62 nearby systems by Planck Collaboration (2011f) are shown for comparison. The masses in the latter two studies were derived from X-ray analyses.…”