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Register a new userFirst Results From an X-ray, Weak Lensing, and Sunyaev-Zeldovich Effect Survey of Nearby Clusters: Abell 3266
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As part of a combined Sunyaev-Zeldovich Effect (SZE), X-ray and weak lensing survey of low redshift (z<0.1) X-ray clusters, we present SZE images of the z=0.059 X-ray cluster Abell 3266 at three observing frequencies (150, 220, 275 GHz) and after the spectral subtraction of primary Cosmic Microwave Background (CMB) anisotropies. These images were generated using the ACBAR bolometer array operated on the Viper telescope at the South Pole. The multi-frequency data from ACBAR should allow us to overcome one of the main obstacles facing the analysis of SZE observations of nearby clusters, i.e. contamination from primary Cosmic Microwave Background (CMB) anisotropies.
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Uncertainty in the mass-observable scaling relations is currently the limiting factor for galaxy cluster based cosmology. Weak gravitational lensing can provide a direct mass calibration and reduce the mass uncertainty. We present new ground-based weak lensing observations of 19 South Pole Telescope (SPT) selected clusters at redshifts $0.29 leq z leq 0.61$ and combine them with previously reported space-based observations of 13 galaxy clusters at redshifts $0.576 leq z leq 1.132$ to constrain the cluster mass scaling relations with the Sunyaev-Zeldovich effect (SZE), the cluster gas mass mgas, and yx, the product of mgas and X-ray temperature. We extend a previously used framework for the analysis of scaling relations and cosmological constraints obtained from SPT-selected clusters to make use of weak lensing information. We introduce a new approach to estimate the effective average redshift distribution of background galaxies and quantify a number of systematic errors affecting the weak lensing modelling. These errors include a calibration of the bias incurred by fitting a Navarro-Frenk-White profile to the reduced shear using $N$-body simulations. We blind the analysis to avoid confirmation bias. We are able to limit the systematic uncertainties to 5.6% in cluster mass (68% confidence). Our constraints on the mass--X-ray observable scaling relations parameters are consistent with those obtained by earlier studies, and our constraints for the mass--SZE scaling relation are consistent with the simulation-based prior used in the most recent SPT-SZ cosmology analysis. We can now replace the external mass calibration priors used in previous SPT-SZ cosmology studies with a direct, internal calibration obtained on the same clusters.
We provide a new framework for the joint analysis of cluster observations (JACO) using simultaneous fits to X-ray, Sunyaev-Zeldovich (SZ), and weak lensing data. Our method fits the mass models simultaneously to all data, provides explicit separation of the gaseous, dark, and stellar components, and--for the first time--allows joint constraints on all measurable physical parameters. JACO includes additional improvements to previous X-ray techniques, such as the treatment of the cluster termination shock and explicit inclusion of the BCGs stellar mass profile. An application of JACO to the rich galaxy cluster Abell 478 shows excellent agreement among the X-ray, lensing, and SZ data. We find that Abell 478 is consistent with a cuspy dark matter profile with inner slope n=1. Accounting for the stellar mass profile of the BCG allows us to rule out inner dark matter slopes n>1.1 at the 99% confidence level. At large radii, an 1/r^3 asymptotic slope is preferred over an 1/r^4 behavior. All single power law dark matter models are ruled out at greater than the 99% confidence level. JACO shows that self-consistent modeling of multiwavelength data can provide powerful constraints on the shape of the dark profile.
Measuring the intrinsic shape and orientation of dark matter (DM) and intracluster (IC) gas in galaxy clusters is crucial to constraining their formation and evolution, and for enhancing the use of clusters as more precise cosmological probes. Extending our previous works, we present for the first time results from a triaxial joint analysis of the galaxy cluster Abell 1835, by means of X-ray, strong lensing (SL) and Sunyaev Zeldovich (SZ) data. We parametrically reconstruct the full three-dimensional structure (triaxial shape and principal axis orientation) of both the DM and the IC gas, and the level of non-thermal pressure of the IC gas. We find that the intermediate-major and minor-major axis ratios of the DM are 0.71+/-0.08 and 0.59+/-0.05, respectively, and the major axis of the DM halo is inclined with respect to the line of sight at 18.3+/-5.2 deg. We present the first observational measurement of the non-thermal pressure out to R_{200}, which has been evaluated to be a few percent of the total energy budget in the internal regions, while reaching approximately 20% in the outer volumes. We discuss the implications of our method for the viability of the CDM scenario, focusing on the concentration parameter C and the inner slope of the DM gamma in order to test the cold dark matter (CDM) paradigm for structure formation: we measure gamma=1.01+/-0.06 and C=4.32+/-0.44, values which are close to the predictions of the CDM model. The combination of X-ray/SL data at high spatial resolution, capable of resolving the cluster core, with the SZ data, which are more sensitive to the cluster outer volume, allows us to characterize the level and the gradient of the gas entropy distribution and non-thermal pressure out to R_{200}, breaking the degeneracy among the physical models describing the thermal history of the ICM.
The use of galaxy clusters as precision cosmological probes relies on an accurate determination of their masses. However, inferring the relationship between cluster mass and observables from direct observations is difficult and prone to sample selection biases. In this work, we use weak lensing as the best possible proxy for cluster mass to calibrate the Sunyaev-Zeldovich (SZ) effect measurements from the APEX-SZ experiment. For a well-defined (ROSAT) X-ray complete cluster sample, we calibrate the integrated Comptonization parameter, $Y_{rm SZ}$, to the weak-lensing derived total cluster mass, $M_{500}$. We employ a novel Bayesian approach to account for the selection effects by jointly fitting both the SZ Comptonization, $Y_{rm SZ}text{--}M_{500}$, and the X-ray luminosity, $L_{rm x}text{--}M_{500}$, scaling relations. We also account for a possible correlation between the intrinsic (log-normal) scatter of $L_{rm x}$ and $Y_{rm SZ}$ at fixed mass. We find the corresponding correlation coefficient to be $r= 0.47_{-0.35}^{+0.24}$, and at the current precision level our constraints on the scaling relations are consistent with previous works. For our APEX-SZ sample, we find that ignoring the covariance between the SZ and X-ray observables biases the normalization of the $Y_{rm SZ}text{--}M_{500}$ scaling high by $1text{--}2sigma$ and the slope low by $sim 1sigma$, even when the SZ effect plays no role in the sample selection. We conclude that for higher-precision data and larger cluster samples, as anticipated from on-going and near-future cluster cosmology experiments, similar biases (due to intrinsic covariances of cluster observables) in the scaling relations will dominate the cosmological error budget if not accounted for correctly.
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-Zeldovich 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.
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