84 research outputs found
Constraining the Scatter in the Mass-Richness Relation of maxBCG Clusters With Weak Lensing and X-ray Data
We measure the logarithmic scatter in mass at fixed richness for clusters in
the maxBCG cluster catalog, an optically selected cluster sample drawn from
SDSS imaging data. Our measurement is achieved by demanding consistency between
available weak lensing and X-ray measurements of the maxBCG clusters, and the
X-ray luminosity--mass relation inferred from the 400d X-ray cluster survey, a
flux limited X-ray cluster survey. We find \sigma_{\ln
M|N_{200}}=0.45^{+0.20}_{-0.18} (95% CL) at N_{200} ~ 40, where N_{200} is the
number of red sequence galaxies in a cluster. As a byproduct of our analysis,
we also obtain a constraint on the correlation coefficient between \ln Lx and
\ln M at fixed richness, which is best expressed as a lower limit, r_{L,M|N} >=
0.85 (95% CL). This is the first observational constraint placed on a
correlation coefficient involving two different cluster mass tracers. We use
our results to produce a state of the art estimate of the halo mass function at
z=0.23 -- the median redshift of the maxBCG cluster sample -- and find that it
is consistent with the WMAP5 cosmology. Both the mass function data and its
covariance matrix are presented.Comment: 14 pages, 6 figures, submitted to Ap
Analysis of anemia and iron supplementation among glioblastoma patients reveals sex-biased association between anemia and survival
The association between anemia and outcomes in glioblastoma patients is unclear. We analyzed data from 1346 histologically confirmed adult glioblastoma patients in the TriNetX Research Network. Median hemoglobin and hematocrit levels were quantified for 6 months following diagnosis and used to classify patients as anemic or non-anemic. Associations of anemia and iron supplementation of anemic patients with median overall survival (median-OS) were then studied. Among 1346 glioblastoma patients, 35.9% of male and 40.5% of female patients were classified as anemic using hemoglobin-based WHO guidelines. Among males, anemia was associated with reduced median-OS compared to matched non-anemic males using hemoglobin (HR 1.24; 95% CI 1.00-1.53) or hematocrit-based cutoffs (HR 1.28; 95% CI 1.03-1.59). Among females, anemia was not associated with median-OS using hemoglobin (HR 1.00; 95% CI 0.78-1.27) or hematocrit-based cutoffs (HR: 1.10; 95% CI 0.85-1.41). Iron supplementation of anemic females trended toward increased median-OS (HR 0.61; 95% CI 0.32-1.19) although failing to reach statistical significance whereas no significant association was found in anemic males (HR 0.85; 95% CI 0.41-1.75). Functional transferrin-binding assays confirmed sexually dimorphic binding in resected patient samples indicating underlying differences in iron biology. Anemia among glioblastoma patients exhibits a sex-specific association with survival
The stellar mass fraction and baryon content of galaxy clusters and groups
[Abridged] The analysis of a sample of 52 clusters with precise and
hypothesis-parsimonious measurements of mass shows that low mass clusters and
groups are not simple scaled-down versions of their massive cousins in terms of
stellar content: lighter clusters have more stars per unit cluster mass. The
same analysis also shows that the stellar content of clusters and groups
displays an intrinsic spread at a given cluster mass, i.e. clusters are not
similar each other in the amount of stars they contain, not even at a fixed
cluster mass. The stellar mass fraction depends on halo mass with (logarithmic)
slope -0.55+/-0.08 and with 0.15+/-0.02 dex of intrinsic scatter at a fixed
cluster mass. The intrinsic scatter at a fixed cluster mass we determine for
gas mass fractions is smaller, 0.06+/-0.01 dex. The intrinsic scatter in both
the stellar and gas mass fractions is a distinctive signature that the regions
from which clusters and groups collected matter, a few tens of Mpc, are yet not
representative, in terms of gas and baryon content, of the mean matter content
of the Universe. The observed stellar mass fraction values are in marked
disagreement with gasdynamics simulations with cooling and star formation of
clusters and groups. We found the the baryon (gas+stellar) fraction is fairly
constant for clusters and groups with 13.7<lg(mass)<15.0 solar masses and it is
offset from the WMAP-derived value by about 6 sigmas. The offset could be
related to the possible non universality of the baryon fraction pointed out by
our measurements of the intrinsic scatter. Our analysis is the first that does
not assume that clusters are identically equal at a given halo mass and it is
also more accurate in many aspects. The data and code used for the stochastic
computation are distributed with the paper.Comment: MNRAS, in pres
The impact of lens galaxy environments on the image separation distribution
We study the impact of lens galaxy environments on the image separation
distribution of lensed quasars. We account for both environmental convergence
and shear, using a joint distribution derived from galaxy formation models
calibrated by galaxy-galaxy lensing data and number counts of massive
elliptical galaxies. We find that the external field enhances lensing
probabilities, particularly at large image separations; the increase is ~30% at
\theta=3'' and ~200% at \theta=5'', when we adopt a power-law source luminosity
function \Phi(L) \propto L^-2.1. The enhancement is mainly driven by
convergence, which boosts both the image separation and magnification bias (for
a fixed lens galaxy mass). These effects have been neglected in previous
studies of lens statistics. Turning the problem around, we derive the posterior
convergence and shear distributions and point out that they are strong
functions of image separation; lens systems with larger image separations are
more likely to lie in dense environments.Comment: 8 pages, 10 figures, accepted for publication in MNRA
Chandra Cluster Cosmology Project II: Samples and X-ray Data Reduction
We discuss the measurements of the galaxy cluster mass functions at z=~0.05
and z=~0.5 using high-quality Chandra observations of samples derived from the
ROSAT PSPC All-Sky and 400deg^2 surveys. We provide a full reference for the
data analysis procedures, present updated calibration of relations between the
total cluster mass and its X-ray indicators (T_X, Mgas, and Y_X) based on a
subsample of low-z relaxed clusters, and present a first measurement of the
evolving L_X-Mtot relation (with Mtot estimated from Y_X) obtained from a
well-defined statistically complete cluster sample and with appropriate
corrections for the Malmquist bias applied. Finally, we present the derived
cluster mass functions, estimate the systematic uncertainties in this
measurement, and discuss the calculation of the likelihood function. We
confidently measure the evolution in the cluster comoving number density at a
fixed mass threshold, e.g., by a factor of 5.0 +- 1.2 at M_500=2.5e14 h^-1 Msun
between z=0 and 0.5. This evolution reflects the growth of density
perturbations and can be used for the cosmological constraints complementing
those from the distance-redshift relation.Comment: ApJ in press (Feb 10, 2009 issue); replacement to match accepted
version, includes revisions in response to referee's and community comment
Parent-children discrepancies in the assessment of childrenâs and adolescentsâ happiness
In this study we assessed parent-child agreement in the perception of a childâs general happiness or well-being in typically developing children (10-11 years-olds; N = 172) and adolescents (15-16 years-olds; N = 185). Despite parent and child reporters providing internally consistent responses in the General Happiness single-item scale and the Oxford Happiness Questionnaire-short form, their perceptions about childrenâs and adolescentsâ general happiness did not correlate. Parents of 10-11 year-olds significantly overestimated childrenâs happiness, supporting previous literature on the parentsâ positivity bias effect. However, parents of 15-16 year-olds showed the reverse pattern, as they underestimated adolescentsâ happiness. Furthermore, parentsâ self-reported happiness or well-being (reported six months later) significantly correlated with their estimations of childrenâs and adolescentsâ happiness. Therefore, these results suggest a potential parentsâ egocentric bias when estimating their childrenâs happiness. These findings are discussed in terms of their theoretical and applied implications for research into child-parent relationships
Estimating cosmological parameters from future gravitational lens surveys
Upcoming ground and space based observatories such as the DES, the LSST, the
JDEM concepts and the SKA, promise to dramatically increase the size of strong
gravitational lens samples. A significant fraction of the systems are expected
to be time delay lenses. Many of the existing lensing degeneracies become less
of an issue with large samples since the distributions of a number of
parameters are predictable, and can be incorporated into an analysis, thus
helping to lessen the degeneracy. Assuming a mean galaxy density profile that
does not evolve with redshift, a Lambda-CDM cosmology, and Gaussian
distributions for bulk parameters describing the lens and source populations,
we generate synthetic lens catalogues and examine the relationship between
constraints on the Omega_m - Omega_Lambda plane and H_0 with increasing lens
sample size. We find that, with sample sizes of ~400 time delay lenses, useful
constraints can be obtained for Omega_m and Omega_Lambda with approximately
similar levels of precision as from the best of other methods. In addition,
sample sizes of ~100 time delay systems yield estimates of H_0 with errors of
only a couple of percent, exceeding the level of precision from current best
estimates such as the HST Key Project. We note that insufficient prior
knowledge of the lens samples employed in the analysis, via under or
overestimates in the mean values of the sample distributions, results in
broadening of constraints. This highlights the need for sound prior knowledge
of the sample before useful cosmological constraints can be obtained from large
time delay samples (abridged).Comment: 10 pages, 3 figures, 1 table. Accepted for publication in MNRA
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the
scale of baryon acoustic oscillations (BAO) in the clustering of matter over a
larger volume than the combined efforts of all previous spectroscopic surveys
of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as
i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7.
Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000
quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5.
Early results from BOSS include the first detection of the large-scale
three-dimensional clustering of the Lyman alpha forest and a strong detection
from the Data Release 9 data set of the BAO in the clustering of massive
galaxies at an effective redshift z = 0.57. We project that BOSS will yield
measurements of the angular diameter distance D_A to an accuracy of 1.0% at
redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the
same redshifts. Forecasts for Lyman alpha forest constraints predict a
measurement of an overall dilation factor that scales the highly degenerate
D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey
is complete. Here, we provide an overview of the selection of spectroscopic
targets, planning of observations, and analysis of data and data quality of
BOSS.Comment: 49 pages, 16 figures, accepted by A
The Atacama Cosmology Telescope: Relation Between Galaxy Cluster Optical Richness and Sunyaev-Zel'dovich Effect
We present the measured Sunyaev-Zel'dovich (SZ) flux from 474
optically-selected MaxBCG clusters that fall within the Atacama Cosmology
Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in
this analysis covers 510 square degrees and overlaps Stripe 82 of the Sloan
Digital Sky Survey. We also present the measured SZ flux stacked on 52
X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an
ACT Southern survey region covering 455 square degrees. We find that the
measured SZ flux from the X-ray-selected clusters is consistent with
expectations. However, we find that the measured SZ flux from the
optically-selected clusters is both significantly lower than expectations and
lower than the recovered SZ flux measured by the Planck satellite. Since we
find a lower recovered SZ signal than Planck, we investigate the possibility
that there is a significant offset between the optically-selected brightest
cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due
to its finer resolution. Such offsets can arise due to either an intrinsic
physical separation between the BCG and the center of the gas concentration or
from misidentification of the cluster BCG. We find that the entire discrepancy
for both ACT and Planck can be explained by assuming that the BCGs are offset
from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc.
Such large offsets between gas peaks and BCGs for optically-selected cluster
samples seem unlikely given that we find the physical separation between BCGs
and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters to have a
much narrower distribution that peaks within 0.2 Mpc. It is possible that other
effects are lowering the ACT and Planck signals by the same amount, with
offsets between BCGs and SZ peaks explaining the remaining difference between
measurements. (Abridged)Comment: 10 pages; version matches that accepted by ApJ - minor additions to
tex
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Dark Energy Survey Year 1 Results: Cross-correlation between Dark Energy Survey Y1 galaxy weak lensing and South Pole Telescope +Planck CMB weak lensing
We cross-correlate galaxy weak lensing measurements from the Dark Energy Survey (DES) year-one data with a cosmic microwave background (CMB) weak lensing map derived from South Pole Telescope (SPT) and Planck data, with an effective overlapping area of 1289 deg2. With the combined measurements from four source galaxy redshift bins, we obtain a detection significance of 5.8Ï. We fit the amplitude of the correlation functions while fixing the cosmological parameters to a fiducial ÎCDM model, finding A=0.99±0.17. We additionally use the correlation function measurements to constrain shear calibration bias, obtaining constraints that are consistent with previous DES analyses. Finally, when performing a cosmological analysis under the ÎCDM model, we obtain the marginalized constraints of Ïm=0.261-0.051+0.070 and S8Ï8Ïm/0.3=0.660-0.100+0.085. These measurements are used in a companion work that presents cosmological constraints from the joint analysis of two-point functions among galaxies, galaxy shears, and CMB lensing using DES, SPT, and Planck data
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