4,557 research outputs found
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 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 structure. The kinetic
energy of the two valence neutrons occupying along the axis is
reduced remarkably due to the strong 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
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
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
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