32,410 research outputs found
CLASH: Weak-Lensing Shear-and-Magnification Analysis of 20 Galaxy Clusters
We present a joint shear-and-magnification weak-lensing analysis of a sample
of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19<z<0.69
selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our
analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam
on the Subaru Telescope. From a stacked shear-only analysis of the
X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a
total signal-to-noise ratio of ~25 in the radial range of 200 to 3500kpc/h. The
stacked tangential-shear signal is well described by a family of standard
density profiles predicted for dark-matter-dominated halos in gravitational
equilibrium, namely the Navarro-Frenk-White (NFW), truncated variants of NFW,
and Einasto models. For the NFW model, we measure a mean concentration of
at . We show this is in excellent agreement with Lambda
cold-dark-matter (LCDM) predictions when the CLASH X-ray selection function and
projection effects are taken into account. The best-fit Einasto shape parameter
is , which is consistent with the
NFW-equivalent Einasto parameter of . We reconstruct projected mass
density profiles of all CLASH clusters from a joint likelihood analysis of
shear-and-magnification data, and measure cluster masses at several
characteristic radii. We also derive an ensemble-averaged total projected mass
profile of the X-ray-selected subsample by stacking their individual mass
profiles. The stacked total mass profile, constrained by the
shear+magnification data, is shown to be consistent with our shear-based
halo-model predictions including the effects of surrounding large-scale
structure as a two-halo term, establishing further consistency in the context
of the LCDM model.Comment: Accepted by ApJ on 11 August 2014. Textual changes to improve clarity
(e.g., Sec.3.2.2 "Number-count Depletion", Sec.4.3 "Shape Measurement",
Sec.4.4 "Background Galaxy Selection"). Results and conclusions remain
unchanged. For the public release of Subaru data, see
http://archive.stsci.edu/prepds/clash
Survey for Transiting Extrasolar Planets in Stellar Systems: III. A Limit on the Fraction of Stars with Planets in the Open Cluster NGC 1245
We analyze a 19-night photometric search for transiting extrasolar planets in
the open cluster NGC 1245. An automated transit search algorithm with
quantitative selection criteria finds six transit candidates; none are bona
fide planetary transits. We characterize the survey detection probability via
Monte Carlo injection and recovery of realistic limb-darkened transits. We use
this to derive upper limits on the fraction of cluster members with close-in
Jupiter-radii, RJ, companions. We carefully analyze the random and systematic
errors of the calculation. For similar photometric noise and weather properties
as this survey, observing NGC 1245 twice as long results in a tighter
constraint on "Hot Jupiter", HJ, companions than observing an additional
cluster of similar richness as NGC 1245 for the same length of time as this
survey. This survey observed ~870 cluster members. If 1% of stars have 1.5 RJ
HJ companions, we expect to detect one planet for every 5000 dwarf stars
observed for a month. To reach a ~2% upper limit on the fraction of stars with
1.5 RJ HJ companions, we conclude a total sample size of ~7400 dwarf stars
observed for at least a month will be needed. Results for 1.0 RJ companions,
without substantial improvement in the photometric precision, will require a
small factor larger sample size.Comment: 24 pages, 15 figures, submitted A
Detection of Enhancement in Number Densities of Background Galaxies due to Magnification by Massive Galaxy Clusters
We present a detection of the enhancement in the number densities of
background galaxies induced from lensing magnification and use it to test the
Sunyaev-Zel'dovich effect (SZE) inferred masses in a sample of 19 galaxy
clusters with median redshift selected from the South Pole
Telescope SPT-SZ survey. Two background galaxy populations are selected for
this study through their photometric colours; they have median redshifts
(low- background) and
(high- background). Stacking these
populations, we detect the magnification bias effect at and
for the low- and high- backgrounds, respectively. We fit NFW
models simultaneously to all observed magnification bias profiles to estimate
the multiplicative factor that describes the ratio of the weak lensing
mass to the mass inferred from the SZE observable-mass relation. We further
quantify systematic uncertainties in resulting from the photometric
noise and bias, the cluster galaxy contamination and the estimations of the
background properties. The resulting for the combined background
populations with uncertainties is
, indicating good consistency
between the lensing and the SZE-inferred masses. We use our best-fit to
predict the weak lensing shear profiles and compare these predictions with
observations, showing agreement between the magnification and shear mass
constraints. This work demonstrates the promise of using the magnification as a
complementary method to estimate cluster masses in large surveys.Comment: 16 pages, 10 figures, accepted for publication in MNRA
A Comparison and Joint Analysis of Sunyaev-Zel'dovich Effect Measurements from Planck and Bolocam for a set of 47 Massive Galaxy Clusters
We measure the SZ signal toward a set of 47 clusters with a median mass of
M and a median redshift of 0.40 using data from
Planck and the ground-based Bolocam receiver. When Planck XMM-like masses are
used to set the scale radius , we find consistency between
the integrated SZ signal, , derived from Bolocam and Planck
based on gNFW model fits using A10 shape parameters, with an average ratio of
(allowing for the % Bolocam flux calibration
uncertainty). We also perform a joint fit to the Bolocam and Planck data using
a modified A10 model with the outer logarithmic slope allowed to vary,
finding (measurement error followed by
intrinsic scatter). In addition, we find that the value of scales with
mass and redshift according to . This mass scaling is in good agreement with recent
simulations. We do not observe the strong trend of with redshift seen
in simulations, though we conclude that this is most likely due to our sample
selection. Finally, we use Bolocam measurements of to test the
accuracy of the Planck completeness estimate. We find consistency, with the
actual number of Planck detections falling approximately below the
expectation from Bolocam. We translate this small difference into a constraint
on the the effective mass bias for the Planck cluster cosmology results, with
.Comment: Updated to include one additional co-author. Also some minor changes
to the text based on initial feedbac
Nonparametric Feature Extraction from Dendrograms
We propose feature extraction from dendrograms in a nonparametric way. The
Minimax distance measures correspond to building a dendrogram with single
linkage criterion, with defining specific forms of a level function and a
distance function over that. Therefore, we extend this method to arbitrary
dendrograms. We develop a generalized framework wherein different distance
measures can be inferred from different types of dendrograms, level functions
and distance functions. Via an appropriate embedding, we compute a vector-based
representation of the inferred distances, in order to enable many numerical
machine learning algorithms to employ such distances. Then, to address the
model selection problem, we study the aggregation of different dendrogram-based
distances respectively in solution space and in representation space in the
spirit of deep representations. In the first approach, for example for the
clustering problem, we build a graph with positive and negative edge weights
according to the consistency of the clustering labels of different objects
among different solutions, in the context of ensemble methods. Then, we use an
efficient variant of correlation clustering to produce the final clusters. In
the second approach, we investigate the sequential combination of different
distances and features sequentially in the spirit of multi-layered
architectures to obtain the final features. Finally, we demonstrate the
effectiveness of our approach via several numerical studies
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