3,298 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
Multispin Coding Technique for Nonequilibrium Reweighting
We present the multispin coding for the nonequlibrium reweighting method of
the Monte Carlo simulation, that was developed by the present authors. As an
illustration, we treat the driven diffusive lattice gas model. We use the
multispin coding technique both for the spin update and for the calculation of
the histogram of incremental weights, which is needed in the calculation of
nonequlibrium reweighting. All the operations are executed by the bitwise
logical commands.Comment: accepted for publication in Int. J. Mod. Phys.
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
Halo-Galaxy Lensing: A Full Sky Approach
The halo-galaxy lensing correlation function or the average tangential shear
profile over sampled halos is a very powerful means of measuring the halo
masses, the mass profile, and the halo-mass correlation function of very large
separations in the linear regime. We reformulate the halo-galaxy lensing
correlation in harmonic space. We find that, counter-intuitively, errors in the
conventionally used flat-sky approximation remain at a % level even at very
small angles. The errors increase at larger angles and for lensing halos at
lower redshifts: the effect is at a few % level at the baryonic acoustic
oscillation scales for lensing halos of , and comparable with the
effect of primordial non-Gaussianity with at large
separations. Our results allow to readily estimate/correct for the full-sky
effect on a high-precision measurement of the average shear profile available
from upcoming wide-area lensing surveys.Comment: 12 pages, 4 figure
Weak Lensing Mass Measurements of Substructures in COMA Cluster with Subaru/Suprime-Cam
We obtain the projected mass distributions for two Subaru/Suprime-Cam fields
in the southwest region (r\simlt 60') of the Coma cluster (z=0.0236) by weak
lensing analysis and detect eight subclump candidates. We quantify the
contribution of background large-scale structure (LSS) on the projected mass
distributions using SDSS multi-bands and photometric data, under the assumption
of mass-to-light ratio for field galaxies. We find that one of eight subclump
candidates, which is not associated with any member galaxies, is significantly
affected by LSS lensing. The mean projected mass for seven subclumps extracted
from the main cluster potential is = (5.06\pm1.30)10^12h^-1 M_sun
after a LSS correction. A tangential distortion profile over an ensemble of
subclumps is well described by a truncated singular-isothermal sphere model and
a truncated NFW model. A typical truncated radius of subclumps, r_t\simeq 35
h^-1 kpc, is derived without assuming any relations between mass and light for
member galaxies. The radius coincides well with the tidal radius, \sim42 h^-1
kpc, of the gravitational force of the main cluster. Taking into account the
incompleteness of data area, a projection effect and spurious lensing peaks, it
is expected that mass of cluster substructures account for 19 percent of the
virial mass, with 13 percent statistical error. The mass fraction of cluster
substructures is in rough agreement with numerical simulations.Comment: ApJ, accepted, 16 pages, 10 figures and 4 tables. High-resolution
pictures available at http://www.asiaa.sinica.edu.tw/~okabe/files/comaWL.pd
Spin Gap in Two-Dimensional Heisenberg Model for CaVO
We investigate the mechanism of spin gap formation in a two-dimensional model
relevant to Mott insulators such as CaVO. From the perturbation
expansion and quantum Monte Carlo calculations, the origin of the spin gap is
ascribed to the four-site plaquette singlet in contrast to the dimer gap
established in the generalized dimerized Heisenberg model.Comment: 8 pages, 6 figures available upon request (Revtex
Can we use Weak Lensing to Measure Total Mass Profiles of Galaxies on 20 kiloparsec Scales?
Current constraints on dark matter density profiles from weak lensing are
typically limited to radial scales greater than 50-100 kpc. In this paper, we
explore the possibility of probing the very inner regions of galaxy/halo
density profiles by measuring stacked weak lensing on scales of only a few tens
of kpc. Our forecasts focus on scales smaller than the equality radius (Req)
where the stellar component and the dark matter component contribute equally to
the lensing signal. We compute the evolution of Req as a function of lens
stellar mass and redshift and show that Req=7-34 kpc for galaxies with the
stellar mass of 10^{9.5}-10^{11.5} solar masses. Unbiased shear measurements
will be challenging on these scales. We introduce a simple metric to quantify
how many source galaxies overlap with their neighbours and for which shear
measurements will be challenging. Rejecting source galaxies with close-by
companions results in about a 20 per cent decrease in the overall source
density. Despite this decrease, we show that Euclid and WFIRST will be able to
constrain galaxy/halo density profiles at Req with signal-to-noise ratio >20
for the stellar mass of >10^{10} solar masses. Weak lensing measurements at
Req, in combination with stellar kinematics on smaller scales, will be a
powerful means by which to constrain both the inner slope of the dark matter
density profile as well as the mass and redshift dependence of the stellar
initial mass function.Comment: 19 pages, 14 figures, 3 tables, submitted to MNRAS, included the
referee comment
Magnetic field generation by the Weibel instability at temperature gradients in collisionless plasmas
The Weibel instability could be responsible for the generation of magnetic
fields in various objects such as gamma-ray bursts, jets from active galactic
nuclei, and clusters of galaxies. Using numerical simulations, the development
of the Weibel instability at a temperature gradient is studied. It is found
that current sheets are first generated at the gradient, and then they are
rounded off and turn into current filaments. During this process, return
currents are generated around the filaments and they prevent filaments from
merger. The magnetic fields around the filaments persist at least until
t~8000/\omega_p, where \omega_p is the plasma frequency, and it is very likely
that they survive for a much longer time.Comment: Physics of Plasmas in pres
ON THE LOW-TEMPERATURE ORDERING OF THE 3D ATIFERROMAGNETIC THREE-STATE POTTS MODEL
The antiferromagnetic three-state Potts model on the simple-cubic lattice is
studied using Monte Carlo simulations. The ordering in a medium temperature
range below the critical point is investigated in detail. Two different regimes
have been observed: The so-called broken sublattice-symmetry phase dominates at
sufficiently low temperatures, while the phase just below the critical point is
characterized by an effectively continuous order parameter and by a fully
restored rotational symmetry. However, the later phase is not the
permutationally sublattice symmetric phase recently predicted by the cluster
variation method.Comment: 20 pages with 9 figures in a single postscript file (compressed and
uuencoded by uufiles -gz -9) plus two big figures in postscript file
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