Subaru weak-lensing study of A2163: bimodal mass structure

We present a weak-lensing analysis of the merging cluster A2163 using Subaru/Suprime-Cam and CFHT/Mega-Cam data and discuss the dynamics of this cluster merger, based on complementary weak-lensing, X-ray, and optical spectroscopic datasets. From two dimensional multi-component weak-lensing analysis, we reveal that the cluster mass distribution is well described by three main components, including a two component main cluster A2163-A with mass ratio 1:8, and its cluster satellite A2163-B. The bimodal mass distribution in A2163-A is similar to the galaxy density distribution, but appears as spatially segregated from the brightest X-ray emitting gas region. We discuss the possible origins of this gas-dark matter offset and suggest the gas core of the A2163-A subcluster has been stripped away by ram pressure from its dark matter component. The survival of this gas core to the tidal forces exerted by the main cluster let us infer a subcluster accretion with a non-zero impact parameter. Dominated by the most massive component of A2163-A, the mass distribution of A2163 is well described by a universal Navarro-Frenk-White profile as shown by a one-dimensional tangential shear analysis, while the singular-isothermal sphere profile is strongly ruled out. Comparing this cluster mass profile with profiles derived assuming intracluster medium hydrostatic equilibrium (H.E.) in two opposite regions of the cluster atmosphere has allowed us to confirm the prediction of a departure from H.E. in the eastern cluster side, presumably due to shock heating. Yielding a cluster mass estimate of M_{500}=11.18_{-1.46}^{+1.64}\times10^{14}h^{-1}Msun, our mass profile confirm the exceptionally high mass of A2163, consistent with previous analyses relying on the cluster dynamical analysis and Yx mass proxy.Comment: 17 pages, 11 figures, ApJ, in press. Full resolution version is available at http://www.asiaa.sinica.edu.tw/~okabe/files/a2163_WL_astroph.pd

Absence of surface mode in a visco-elastic material with surface tension

The surface waves in the visco-elastic media with the surface tension are studied using the Voigt-Kelvin model of the visco-elasticity. It is shown that the surface mode of oscillation does not exist in the parameter region where the effect of surface tension is larger than that of the elastic stress at the surface unless the viscous stress masks the elastic stress in the bulk. In the region, the surface oscillation is suppressed and the oscillation beneath the surface diffuses after the pulse goes into the bulk. The experimental relevance of the present results is also discussed.Comment: 5 pages, 3 figure

Random template banks and relaxed lattice coverings

Template-based searches for gravitational waves are often limited by the computational cost associated with searching large parameter spaces. The study of efficient template banks, in the sense of using the smallest number of templates, is therefore of great practical interest. The "traditional" approach to template-bank construction requires every point in parameter space to be covered by at least one template, which rapidly becomes inefficient at higher dimensions. Here we study an alternative approach, where any point in parameter space is covered only with a given probability < 1. We find that by giving up complete coverage in this way, large reductions in the number of templates are possible, especially at higher dimensions. The prime examples studied here are "random template banks", in which templates are placed randomly with uniform probability over the parameter space. In addition to its obvious simplicity, this method turns out to be surprisingly efficient. We analyze the statistical properties of such random template banks, and compare their efficiency to traditional lattice coverings. We further study "relaxed" lattice coverings (using Zn and An* lattices), which similarly cover any signal location only with probability < 1. The relaxed An* lattice is found to yield the most efficient template banks at low dimensions (n < 10), while random template banks increasingly outperform any other method at higher dimensions.Comment: 13 pages, 10 figures, submitted to PR

High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift

We present an analysis of a Suzaku observation of the link region between the galaxy clusters A399 and A401. We obtained the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determine the metallicity where the virial radii of the two clusters cross each other (~2 Mpc away from their centers) and found that it is comparable to that in their inner regions (~0.2 Zsun). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since the ram-pressure is too small to strip the interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity that we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also searched for the oxygen emission from the warm--hot intergalactic medium in that region and obtained a strict upper limit of the hydrogen density (nH<4.1x10^-5 cm^-3).Comment: Typo corrected. The published version is available on-line free of charge by the end of 2008. http://pasj.asj.or.jp/v60/sp1/60s133/60s133.pd

Important role of the spin-orbit interaction in forming the 1/2^+ orbital structure in Be isotopes

The structure of the second 0^+ state of ^{10}Be is investigated using a microscopic $\alpha+\alpha+n+n$ model based on the molecular-orbit (MO) model. The second 0^+ state, which has dominantly the (1/2^+)^2 configuration, is shown to have a particularly enlarged $\alpha-\alpha$ structure. The kinetic energy of the two valence neutrons occupying along the $\alpha-\alpha$ axis is reduced remarkably due to the strong $\alpha$ clustering and, simultaneously, the spin-orbit interaction unexpectedly plays important role to make the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between 1^- and 2^- (~ 300 keV) is found to be an evidence of this spin-mixing effect. ^{12}{Be} is also investigated using $\alpha+\alpha+4n$ model, in which four valence neutrons are considered to occupy the (3/2^-)^2(1/2^+)^2 configuration. The energy surface of ^{12}Be is shown to exhibit similar characteristics, that the remarkable $\alpha$ clustering and the contribution of the spin-orbit interaction make the binding of the state with (3/2^-)^2(1/2^+)^2 configuration properly stronger in comparison with the closed p-shell (3/2^-)^2(1/2^-)^2 configuration.Comment: 14 pages, 4 figure