332 research outputs found
Cross-correlation Weak Lensing of SDSS galaxy Clusters II: Cluster Density Profiles and the Mass--Richness Relation
We interpret and model the statistical weak lensing measurements around
130,000 groups and clusters of galaxies in the Sloan Digital Sky Survey
presented by Sheldon et al. 2007 (Paper I). We present non-parametric
inversions of the 2D shear profiles to the mean 3D cluster density and mass
profiles in bins of both optical richness and cluster i-band luminosity. We
correct the inferred 3D profiles for systematic effects, including non-linear
shear and the fact that cluster halos are not all precisely centered on their
brightest galaxies. We also model the measured cluster shear profile as a sum
of contributions from the brightest central galaxy, the cluster dark matter
halo, and neighboring halos. We infer the relations between mean cluster virial
mass and optical richness and luminosity over two orders of magnitude in
cluster mass; the virial mass at fixed richness or luminosity is determined
with a precision of 13% including both statistical and systematic errors. We
also constrain the halo concentration parameter and halo bias as a function of
cluster mass; both are in good agreement with predictions of LCDM models. The
methods employed here will be applicable to deeper, wide-area optical surveys
that aim to constrain the nature of the dark energy, such as the Dark Energy
Survey, the Large Synoptic Survey Telescope and space-based surveys
Auswahl der hier zu Lande zu pflanzenden Obstbäume / vom ... [Theodor] Engelbrecht. - (Extra-Blatt der Zeitschrift des Hannoverschen pomologischen Vereins ; September 1866)
Optimierungspotentiale der ökonomischen Stickstoff-Effizienz: Segmentierung ausgewählter Ökolandbau-Betriebe mittels Clusteranalyse
Die Heterogenität von Ökobetrieben erschwert die Identifikation von Faktoren für ein optimiertes Nährstoffmanagement. Mittels Clusteranalyse werden in diesem Beitrag ausgewählte Ökobetriebe segmentiert und damit die Grundlage für eine verbesserte Analyse der ökonomischen N-Effizienz geschaffen
Strain-specific requirement for eosinophils in the recruitment of T cells to the lung during the development of allergic asthma
Eosinophils have been implicated as playing a major role in allergic airway responses. However, the importance of these cells to the development of this disease has remained ambiguous despite many studies, partly because of lack of appropriate model systems. In this study, using transgenic murine models, we more clearly delineate a role for eosinophils in asthma. We report that, in contrast to results obtained on a BALB/c background, eosinophil-deficient C57BL/6 ΔdblGATA mice (eosinophil-null mice via the ΔDblGATA1 mutation) have reduced airway hyperresponsiveness, and cytokine production of interleukin (IL)-4, -5, and -13 in ovalbumin-induced allergic airway inflammation. This was caused by reduced T cell recruitment into the lung, as these mouse lungs had reduced expression of CCL7/MCP-3, CC11/eotaxin-1, and CCL24/eotaxin-2. Transferring eosinophils into these eosinophil-deficient mice and, more importantly, delivery of CCL11/eotaxin-1 into the lung during the development of this disease rescued lung T cell infiltration and airway inflammation when delivered together with allergen. These studies indicate that on the C57BL/6 background, eosinophils are integral to the development of airway allergic responses by modulating chemokine and/or cytokine production in the lung, leading to T cell recruitment
MaxBCG: A Red Sequence Galaxy Cluster Finder
Measurements of galaxy cluster abundances, clustering properties, and mass
to- light ratios in current and future surveys can provide important
cosmological constraints. Digital wide-field imaging surveys, the
recently-demonstrated fidelity of red-sequence cluster detection techniques,
and a new generation of realistic mock galaxy surveys provide the means for
construction of large, cosmologicallyinteresting cluster samples, whose
selection and properties can be understood in unprecedented depth. We present
the details of the "maxBCG" algorithm, a cluster-detection technique tailored
to multi-band CCD-imaging data. MaxBCG primarily relies on an observational
cornerstone of massive galaxy clusters: they are marked by an overdensity of
bright, uniformly red galaxies. This detection scheme also exploits classical
brightest cluster galaxies (BCGs), which are often found at the center of these
same massive clusters. (ABRIDGED)Comment: 39 pages, 16 figures, 1 table. Accepted to Ap
Cosmological Constraints from SDSS maxBCG Cluster Abundances
We perform a maximum likelihood analysis of the cluster abundance measured in
the SDSS using the maxBCG cluster finding algorithm. Our analysis is aimed at
constraining the power spectrum normalization , and assumes flat
cosmologies with a scale invariant spectrum, massless neutrinos, and CMB and
supernova priors Omega_m*h^2=0.128+/-0.01 and h=0.72+/-0.05 respectively.
Following the method described in the companion paper Rozo et al. 2007, we
derive \sigma_8=0.92+/-0.10$ (1-sigma) after marginalizing over all major
systematic uncertainties. We place strong lower limits on the normalization,
sigma_8>0.76 (95% CL) (>0.68 at 99% CL). We also find that our analysis favors
relatively low values for the slope of the Halo Occupation Distribution (HOD),
alpha=0.83+/-0.06. The uncertainties of these determinations will substantially
improve upon completion of an ongoing campaign to estimate dynamical, weak
lensing, and X-ray cluster masses in the SDSS maxBCG cluster sample.Comment: 10 pages, 6 figures, ApJ Submitte
Extrinsic Sources of Scatter in the Richness-Mass Relation of Galaxy Clusters
Maximizing the utility of upcoming photometric cluster surveys requires a
thorough understanding of the richness-mass relation of galaxy clusters. We use
Monte Carlo simulations to study the impact of various sources of observational
scatter on this relation. Cluster ellipticity, photometric errors, photometric
redshift errors, and cluster-to-cluster variations in the properties of
red-sequence galaxies contribute negligible noise. Miscentering, however, can
be important, and likely contributes to the scatter in the richness-mass
relation of galaxy maxBCG clusters at the low mass end, where centering is more
difficult. We also investigate the impact of projection effects under several
empirically motivated assumptions about cluster environments. Using SDSS data
and the maxBCG cluster catalog, we demonstrate that variations in cluster
environments can rarely (\approx 1% - 5% of the time) result in significant
richness boosts. Due to the steepness of the mass/richness function, the
corresponding fraction of optically selected clusters that suffer from these
projection effects is \approx 5% - 15%. We expect these numbers to be generic
in magnitude, but a precise determination requires detailed, survey-specific
modeling
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
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