116 research outputs found
GaBoDS: The Garching-Bonn Deep Survey -- IX. A sample of 158 shear-selected mass concentration candidates
The aim of the present work is the construction of a mass-selected galaxy
cluster sample based on weak gravitational lensing methods. This sample will be
subject to spectroscopic follow-up observations.
We apply the mass aperture statistics and a derivative of it to 19 square
degrees of high quality, single colour wide field imaging data obtained with
the WFI@MPG/ESO 2.2m telescope. For the statistics a family of filter functions
is used that approximates the expected tangential radial shear profile and thus
allows for the efficient detection of mass concentrations.
We identify 158 possible mass concentrations. This is the first time that
such a large and blindly selected sample is published. 72 of the detections are
associated with concentrations of bright galaxies. For about 22 of those we
found spectra in the literature, indicating or proving that the galaxies seen
are indeed spatially concentrated. 15 of those were previously known to be
clusters or have meanwhile been secured as such. We currently follow-up a
larger number of them spectroscopically to obtain deeper insight into their
physical properties. The remaining 55% of the possible mass concentrations
found are not associated with any optical light, or could not be classified
unambiguously. We show that those "dark" detections are to a significant degree
due to noise, and appear preferentially in shallow data.Comment: 25 pages, 18 figures, submitted to A&A; for a better print version,
see http://www.astro.uni-bonn.de/~mischa/astroph_0607022.pd
INHIBITORY DIMENSIONAL CONTROL IN THE PIGEON: THE EFFECTS OF DISCRIMINATIVE AUTOSHAPING AND NEGATIVE AUTOMAINTENANCE PROCEDURES
The 400d Galaxy Cluster Survey weak lensing programme: II: Weak lensing study of seven clusters with MMT/Megacam
Evolution in the mass function of galaxy clusters sensitively traces both the
expansion history of the Universe and cosmological structure formation. Robust
cluster mass determinations are a key ingredient for a reliable measurement of
this evolution, especially at high redshift. Weak gravitational lensing is a
promising tool for, on average, unbiased mass estimates. This weak lensing
project aims at measuring reliable weak lensing masses for a complete X-ray
selected sample of 36 high redshift (0.35<z<0.9) clusters. The goal of this
paper is to demonstrate the robustness of the methodology against commonly
encountered problems, including pure instrumental effects, the presence of
bright (8--9 mag) stars close to the cluster centre, ground based measurements
of high-z (z~0.8) clusters, and the presence of massive unrelated structures
along the line-sight. We select a subsample of seven clusters observed with
MMT/Megacam. Instrumental effects are checked in detail by cross-comparison
with an archival CFHT/MegaCam observation. We derive mass estimates for seven
clusters by modelling the tangential shear with an NFW profile, in two cases
with multiple components to account for projected structures in the
line-of-sight. We firmly detect lensing signals from all seven clusters at more
than and determine their masses, ranging from
to , despite the presence of nearby bright stars. We
retrieve the lensing signal of more than one cluster in the CL 1701+6414 field,
while apparently observing CL 1701+6414 through a massive foreground filament.
We also find a multi-peaked shear signal in CL 1641+4001. Shear structures
measured in the MMT and CFHT images of CL 1701+6414 are highly correlated.Comment: Accepted for publication in Astronomy & Astrophysics; A&A 546, A7
Die Entwicklung des Arzneimittelverbrauchs unter besonderer Berücksichtigung demographischer Faktoren
How accurately can we measure weak gravitational shear?
With the recent detection of cosmic shear, the most challenging effect of
weak gravitational lensing has been observed. The main difficulties for this
detection were the need for a large amount of high quality data and the control
of systematics during the gravitational shear measurement process, in
particular those coming from the Point Spread Function anisotropy. In this
paper we perform detailed simulations with the state-of-the-art algorithm
developed by Kaiser, Squires and Broadhurst (KSB) to measure gravitational
shear. We show that for realistic PSF profiles the KSB algorithm can recover
any shear amplitude in the range 0.012 < |\gammavec |<0.32 with a relative,
systematic error of . We give quantitative limits on the PSF correction
method as a function of shear strength, object size, signal-to-noise and PSF
anisotropy amplitude, and we provide an automatic procedure to get a reliable
object catalog for shear measurements out of the raw images.Comment: 23 pages LaTeX, 17 Figures, inclusion of referee comments, published
by A&A Main Journal (366, 717-735
Einfluß demographischer Änderungen auf Fallzahlen und Pflegetage hospitalisierter internistischer Patienten
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