18,899 research outputs found
CLASH: Mass Distribution in and around MACS J1206.2-0847 from a Full Cluster Lensing Analysis
We derive an accurate mass distribution of the galaxy cluster MACS
J1206.2-0847 (z=0.439) from a combined weak-lensing distortion, magnification,
and strong-lensing analysis of wide-field Subaru BVRIz' imaging and our recent
16-band Hubble Space Telescope observations taken as part of the Cluster
Lensing And Supernova survey with Hubble (CLASH) program. We find good
agreement in the regions of overlap between several weak and strong lensing
mass reconstructions using a wide variety of modeling methods, ensuring
consistency. The Subaru data reveal the presence of a surrounding large scale
structure with the major axis running approximately north-west south-east
(NW-SE), aligned with the cluster and its brightest galaxy shapes, showing
elongation with a \sim 2:1 axis ratio in the plane of the sky. Our full-lensing
mass profile exhibits a shallow profile slope dln\Sigma/dlnR\sim -1 at cluster
outskirts (R>1Mpc/h), whereas the mass distribution excluding the NW-SE excess
regions steepens further out, well described by the Navarro-Frenk-White form.
Assuming a spherical halo, we obtain a virial mass M_{vir}=(1.1\pm 0.2\pm
0.1)\times 10^{15} M_{sun}/h and a halo concentration c_{vir} = 6.9\pm 1.0\pm
1.2 (\sim 5.7 when the central 50kpc/h is excluded), which falls in the range
4 <7 of average c(M,z) predictions for relaxed clusters from recent Lambda
cold dark matter simulations. Our full lensing results are found to be in
agreement with X-ray mass measurements where the data overlap, and when
combined with Chandra gas mass measurements, yield a cumulative gas mass
fraction of 13.7^{+4.5}_{-3.0}% at 0.7Mpc/h (\approx 1.7r_{2500}), a typical
value observed for high mass clusters.Comment: Accepted by ApJ (30 pages, 17 figures), one new figure (Figure 10)
added, minor text changes; a version with high resolution figures available
at http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/MACS1206/ms_highreso.pd
Using galaxy-galaxy weak lensing measurements to correct the Finger-of-God
For decades, cosmologists have been using galaxies to trace the large-scale
distribution of matter. At present, the largest source of systematic
uncertainty in this analysis is the challenge of modeling the complex
relationship between galaxy redshift and the distribution of dark matter. If
all galaxies sat in the centers of halos, there would be minimal Finger-of-God
(FoG) effects and a simple relationship between the galaxy and matter
distributions. However, many galaxies, even some of the luminous red galaxies
(LRGs), do not lie in the centers of halos. Because the galaxy-galaxy lensing
is also sensitive to the off-centered galaxies, we show that we can use the
lensing measurements to determine the amplitude of this effect and to determine
the expected amplitude of FoG effects. We develop an approach for using the
lensing data to model how the FoG suppresses the power spectrum amplitudes and
show that the current data implies a 30% suppression at wavenumber k=0.2h/Mpc.
Our analysis implies that it is important to complement a spectroscopic survey
with an imaging survey with sufficient depth and wide field coverage. Joint
imaging and spectroscopic surveys allow a robust, unbiased use of the power
spectrum amplitude information: it improves the marginalized error of growth
rate fg=dln D/dln a by up to a factor of 2 over a wide range of redshifts
z<1.4. We also find that the dark energy equation-of-state parameter, w0, and
the neutrino mass, fnu, can be unbiasedly constrained by combining the lensing
information, with an improvement of 10--25% compared to a spectroscopic survey
without lensing calibration.Comment: 26 pages, 13 figures, accepted for publication in MNRA
Impact of lens distrortions on strain measurements obtained with digital image correlation
The determination of strain fields based on displacements obtained via DIC at the micro-strain level is still a cumbersome task. In particular when high-strain gradients are involved, e.g. in composite materials with multidirectional fibre reinforcement, uncertainties in the experimental setup and errors in the derivation of the displacement fields can substantially hamper the strain identification process. In this contribution, the aim is to investigate the impact of lens distortions on strain measurements. To this purpose, we first perform pure rigid body motion experiments, revealing the importance of precise correction of lens distortions. Next, a uni-axial tensile test on a textile composite with spatially varying high strain gradients is performed, resulting in very accurate determined strains along the fibers of the materia
Using Weak Lensing Dilution to Improve Measurements of the Luminous and Dark Matter in A1689
The E/SO sequence of a cluster defines a boundary redward of which a reliable
weak lensing signal can be obtained from background galaxies, uncontaminated by
cluster members. For bluer colors, both background and cluster members are
present, reducing the distortion signal by the proportion of unlensed cluster
members. In deep Subaru and HST/ACS images of A1689 the tangential distortion
of galaxies with bluer colors falls rapidly toward the cluster center relative
to the lensing signal of the red background. We use this dilution effect to
derive the cluster light profile and luminosity function to large radius, with
the advantage that no subtraction of far-field background counts is required.
The light profile declines smoothly to the limit of the data, r<2Mpc/h, with a
constant slope, dlog(L)/dlog(r)=-1.12+-0.06, unlike the lensing mass profile
which steepens continuously with radius, so that M/L peaks at an intermediate
radius, ~100kpc/h. A flatter behavior is found for the more physically
meaningful ratio of dark-matter to stellar-matter, when accounting for the
color-mass relation of cluster members. The cluster luminosity function has a
flat slope, alpha=-1.05+-0.07, independent of radius and with no faint upturn
to M_i'<-12. We establish that the very bluest objects are negligibly
contaminated by the cluster V-i'<0.2, because their distortion profile rises
towards the center following the red background, but offset higher by ~20%.
This larger amplitude is consistent with the greater estimated depth of the
faint blue galaxies, z~=2.0 compared to z~=0.85 for the red background, a
purely geometric effect related to cosmological parameters. Finally, we improve
upon our earlier mass profile by combining both the red and blue background
populations, clearly excluding low concentration CDM profiles.Comment: 17 pages, 21 figures, revised version in response to referee
comments,(added some discussion, references), conclusions unchanged. Accepted
for publication in Ap
The Mass Structure of the Galaxy Cluster Cl0024+1654 from a Full Lensing Analysis of Joint Subaru and ACS/NIC3 Observations
We derive an accurate mass distribution of the rich galaxy cluster
Cl0024+1654 (z=0.395) based on deep Subaru BR_{c}z' imaging and our recent
comprehensive strong lensing analysis of HST/ACS/NIC3 observations. We obtain
the weak lensing distortion and magnification of undilted samples of red and
blue background galaxies by carefully combining all color and positional
information. Unlike previous work, the weak and strong lensing are in excellent
agreement where the data overlap. The joint mass profile continuously steepens
out to the virial radius with only a minor contribution \sim 10% in the mass
from known subcluster at a projected distance of \sim 700kpc/h. The projected
mass distribution for the entire cluster is well fitted with a single
Navarro-Frenk-White model with a virial mass, M_{vir} = (1.2 \pm 0.2) \times
10^{15} M_{sun}/h, and a concentration, c_{vir} = 9.2^{+1.4}_{-1.2}. This model
fit is fully consistent with the depletion of the red background counts,
providing independent confirmation. Careful examination and interpretation of
X-ray and dynamical data strongly suggest that this cluster system is in a post
collision state, which we show is consistent with our well-defined mass profile
for a major merger occurring along the line of sight, viewed approximately
2-3Gyr after impact when the gravitational potential has had time to relax in
the center, before the gas has recovered and before the outskirts are fully
virialized. Finally, our full lensing analysis provides a model-independent
constraint of M_{2D}(<r_{vir}) = (1.4 \pm 0.3) \times 10^{15} M_{sun}/h for the
projected mass of the whole system, including any currently unbound material
beyond the virial radius, which can constrain the sum of the two pre-merger
cluster masses when designing simulations to explore this system.Comment: Accepted by ApJ; 35 pages, 25 figures; including gNFW fit results
(Section 5.1), simulated post-shock temperatures consistent with X-ray
results using T_{sl} (Section 7.3); Figures 7, 16, 24 added; a version with
high resolution figures available at
http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/CL0024/ms_highreso.pd
Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies
The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1- error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1- of the cosmic variance of mock
samples in the wavenumber range h Mpc. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions for SCDM and
CDM models are also consistent with other detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for
publication in Ap
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