13627338
Subaru Weak Lensing Study of Seven Merging Clusters: Distributions of Mass and Baryons
We present and compare projected distributions of mass, galaxies, and the intracluster medium (ICM) for a sample of merging clusters of galaxies based on the joint weak-lensing, optical photometric, and X-ray analysis. Our sample comprises seven nearby Abell clusters, for which we have conducted systematic, deep imaging observations with Suprime-Cam on Subaru telescope. Our seven target clusters, representing various merging stages and conditions, allow us to investigate in details the physical interplay between dark matter, ICM, and galaxies associated with cluster formation and evolution. A1750 and A1758 are binary systems consisting of two cluster-sized components, A520, A754, A1758N, A1758S, and A1914 are on-going cluster mergers, and A2034 and A2142 are cold-front clusters. In the binary clusters, the projected mass, optical light, and X-ray distributions are overall similar and regular without significant substructures. On-going and cold-front merging clusters, on the other hand, reveal highly irregular mass distributions. Overall the mass distribution appears to be similar to the galaxy luminosity distribution, whereas their distributions are quite different from the ICM distribution in a various ways. We also measured for individual targets the global cluster parameters such as the cluster mass,the mass-to-light ratio, and the ICM temperature. A comparison of the ICM and virial temperatures of merging clusters from X-ray and weak-lensing analyses, respectively, shows that the ICM temperature of on-going and cold-front clusters is significantly higher than the cluster virial temperature by a factor of $\sim 2$. This temperature excess in the ICM could be explained by the effects of merger boosts.
7969431
How Well Can Weak Lensing Measure the Mass of Galaxy Clusters
The technique of weak-lensing aperture mass densitometry, so called the zeta-statistic, has recently been popular in actual observations for measurement of individual cluster mass. It has however been anticipated that the line-of-sight projection by foreground and background matter can adversely affect the cluster mass determination with not only substantial error dispersion but also a sizable positive systematic bias. Additionally, the finite number of background galaxies even at a reasonable observing depth can also introduce Poisson noise to the mass estimate. In this paper, we quantitatively investigate the degree of errors separately contributed by the two sources to the mass determination of those galaxy clusters with M_{200}>10^{14}M_{\odot}. We find that the aperture mass of zeta-statistic turns out to be a mass estimator of much reduced systematic bias, due to the cancellation by the positively biased local background mass sheet. However, the error dispersion of M_{200} arising from both projection effect and Poisson noise is found to be still sizable (40%-90%), even for the shear-selected, clean sample where multiple clusters located within a suitable projected aperture are removed. We also investigate how to remedy this large-error problem in weak lensing measurements, and propose a plausible alternative mass estimator, M(<theta_{1000}), an aperture mass measured within about half the virial radius. The aperture mass M(<theta_{1000}) is free of bias and has a substantially reduced error dispersion, 39% for the worst case of high-z, low-mass clusters, that can be smaller than the error dispersion of M_{200} as much as a factor 3.
16007678
AMiBA WIDEBAND ANALOG CORRELATOR
A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array for Microwave Background Anisotropy. Lag correlators using analog multipliers provide large bandwidth and moderate frequency resolution. Broadband intermediate frequency distribution, back-end signal processing, and control are described. Operating conditions for optimum sensitivity and linearity are discussed. From observations, a large effective bandwidth of around 10 GHz has been shown to provide sufficient sensitivity for detecting cosmic microwave background variations.
59408988
Full lensing analysis of Abell 1703: comparison of independent lens-modelling techniques
The inner mass-prole of the relaxed cluster Abell 1703 is analysed by two very dierent strong-lensing techniques applied to deep ACS and WFC3 imaging. Our parametric method has the accuracy required to reproduce the many sets of multiple images, based on the assumption that mass approximately traces light. We test this assumption with a fully non-parametric, adaptive grid method, with no knowledge of the galaxy distribution. Dierences between the methods are seen on
42818858
Cluster–cluster lensing and the case of Abell 383
Extensive surveys of galaxy clusters motivate us to assess the likelihood of cluster–cluster lensing (CCL), namely, gravitational lensing of a background cluster by a foreground cluster. We briefly describe the characteristics of CCLs in optical, X-ray and Sunyaev–Zel'dovich effect measurements, and calculate their predicted numbers for Λ cold dark matter (ΛCDM) parameters and a viable range of cluster mass functions and their uncertainties. The predicted number of CCLs in the strong-lensing regime varies from several (<10) to as high as a few dozen, depending mainly on whether lensing triaxiality bias is accounted for, through the c–M relation. A much larger number is predicted when taking into account also CCL in the weak-lensing regime. In addition to few previously suggested CCLs, we report a detection of a possible CCL in A383, where background candidate high-z structures are magnified, as seen in deep Subaru observations.
119110258
AMiBA: Sunyaev-Zel'dovich effect derived properties and scaling relations of massive galaxy clusters
The Sunyaev-Zel'dovich Effect (SZE) has been observed toward six massive galaxy clusters, at redshifts 0.091 ≤ z ≤ 0.322 in the 86-102 GHz band with the Y. T. Lee Array for Microwave Background Anisotropy (AMiBA). We modify an iterative method, based on the isothermal β models, to derive the electron temperature T e, total mass M t, gas mass M g, and integrated Compton Y within r 2500, from the AMiBA SZE data. Non-isothermal universal temperature profile (UTP) β models are also considered in this paper. These results are in good agreement with those deduced from other observations. We also investigate the embedded scaling relations, due to the assumptions that have been made in the method we adopted, between these purely SZE-deduced T e, M t, M g, and Y. Our results suggest that cluster properties may be measurable with SZE observations alone. However, the assumptions built into the pure-SZE method bias the results of scaling relation estimations and need further study.
18702340
SUBARU MID-INFRARED IMAGING OF THE QUADRUPLE LENSES PG 1115+080 AND B1422+231: LIMITS ON SUBSTRUCTURE LENSING
We present mid-infrared imaging at 11.7 μm for the quadruple lens systems PG 1115+080 and B1422+231 using the cooled mid-infrared camera and spectrometer (COMICS) attached on the Subaru Telescope. These lensed QSOs are characterized by their anomalous optical and radio flux ratios, as obtained for A1 and A2 images of PG 1115+080 and A, B, and C images of B1422+231, respectively, i.e., such flux ratios are hardly able to be reproduced by lens models with a smooth mass distribution. Our mid-infrared observations for these images have revealed that the mid-infrared flux ratio A2/A1 of PG 1115+080 is virtually consistent with smooth lens models (but inconsistent with the optical flux ratio), whereas for B1422+231, the mid-infrared flux ratios among the A, B, and C images are in good agreement with the radio flux ratios. We also identify a clear infrared bump in the spectral energy distributions of these QSOs, thereby indicating that the observed mid-infrared fluxes originate from a hot dust torus around a QSO nucleus. Based on the size estimate of the dust torus, we place limits on the mass of a substructure in these lens systems causing the anomalous optical or radio flux ratios. For PG 1115+080, the mass of a substructure inside an Einstein radius ME is 16 M☉, corresponding to either a star or a low-mass CDM subhalo having a mass of M 2.2 × 104 M☉ inside a radius of 100 pc if modeled as a singular isothermal sphere (SIS). For B1422+231, we obtain ME 209 M☉, indicating that a CDM subhalo is more likely, having a mass of M 7.4 × 104 M☉.