910 research outputs found
Studying the Nature of Dark Energy with Galaxy Clusters
We report on the status of our effort to constrain the nature of dark energy
through the evolution of the cluster mass function. Chandra temperature
profiles for 31 clusters from a local cluster sample are shown. The X-ray
appearance of the proto supermassive binary black hole at the center of the
cluster Abell 400 is described. Preliminary weak lensing results obtained with
Megacam@MMT for a redshift z=0.5 cluster from a distant cluster sample are
given.Comment: 5 pages, to appear in: Aschenbach, B., Burwitz, V., Hasinger, G.,
Leibundgut, B. (eds.), Relativistic Astrophysics and Cosmology - Einstein's
Legacy. ESO Astrophysics Symposia, Springer Verlag, Berlin, German
Detection of Dark Matter Concentrations in the Field of Cl 1604+4304 from Weak Lensing Analysis
We present a weak-lensing analysis of a region around the galaxy cluster Cl
1604+4304 (z=0.897) on the basis of the deep observations with the HST/WFPC2.
We apply a variant of Schneider's aperture mass technique to the observed WFPC2
field and obtain the distribution of weak-lensing signal-to-noise (S/N) ratio
within the field. The resulting S/N map reveals a clear pronounced peak located
about 1.7 arcmin (850h_{50}^{-1} kpc at z=0.897) southwest of the second peak
associated with the optical cluster center determined from the dynamical
analysis of Postman et al. A non-linear finite-field inversion method has been
used to reconstruct the projected mass distribution from the observed shear
field. The reconstructed mass map shows a super-critical feature at the
location of the S/N peak as well as in the cluster central region. Assuming the
redshift distribution of field galaxies, we obtain the total mass in the
observed field to be 1.0 h_{50}^{-1} 10^{15} M_sun for =1.0. The estimated
mass within a circular aperture of radius 280h_{50}^{-1} kpc centered on the
dark clump is 2.4h_{50}^{-1} 10^{14} M_sun. We have confirmed the existence of
the ` dark ' mass concentration from another deep HST observation with a
slightly different ~20 arcsec pointing.Comment: 7 pages, 3 figure
GaBoDS: The Garching-Bonn Deep Survey -- I. Anatomy of galaxy clusters in the background of NGC 300
The Garching-Bonn Deep Survey (GaBoDS) is a virtual 12 square degree cosmic
shear and cluster lensing survey, conducted with the [email protected] MPG/ESO telescope
at La Silla. It consists of shallow, medium and deep random fields taken in
R-band in subarcsecond seeing conditions at high galactic latitude. A
substantial amount of the data was taken from the ESO archive, by means of a
dedicated ASTROVIRTEL program.
In the present work we describe the main characteristics and scientific goals
of GaBoDS. Our strategy for mining the ESO data archive is introduced, and we
comment on the Wide Field Imager data reduction as well. In the second half of
the paper we report on clusters of galaxies found in the background of NGC 300,
a random archival field. We use weak gravitational lensing and the red cluster
sequence method for the selection of these objects. Two of the clusters found
were previously known and already confirmed by spectroscopy. Based on the
available data we show that there is significant evidence for substructure in
one of the clusters, and an increasing fraction of blue galaxies towards larger
cluster radii. Two other mass peaks detected by our weak lensing technique
coincide with red clumps of galaxies. We estimate their redshifts and masses.Comment: 20 pages, 16 figures, gzipped. An online postscript version with
higher quality figures (3.3 MBytes) can be downloaded from
http://www.mpa-garching.mpg.de/~mischa/ngc300/ngc300.ps.gz . Submitted to A&
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We have shown that the cluster-mass reconstruction method
which combines strong and weak gravitational lensing data, developed
in the first paper in the series, successfully reconstructs the
mass distribution of a simulated cluster. In this paper we apply the method to the
ground-based high-quality multi-colour data of RX J1347.5-114
ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees
In this paper the list of candidate clusters identified from the I-band data
of the ESO Imaging Survey (EIS) is completed using the images obtained over a
total area of about 12 square degrees. Together with the data reported earlier
the total I-band coverage of EIS is 17 square degrees, which has yielded a
sample of 252 cluster candidates in the redshift range 0.2 \lsim z \lsim 1.3.
This is the largest optically-selected sample currently available in the
Southern Hemisphere. It is also well distributed in the sky thus providing
targets for a variety of VLT programs nearly year round.Comment: 5 pages, 3 figures, submitted to Astronomy & Astrophysic
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ARCRAIDER II: Arc search in a sample of non-Abell clusters
We present a search for gravitational arcs in a sample of X-ray luminous,
medium redshift clusters of galaxies. The sample of clusters is called
ARCRAIDER, is based on the ROSAT Bright Survey (RBS) and fulfills the following
criteria: (a) X-ray luminosity Lx>=0.5x10^45erg/s (0.5-2keV band), (b) redshift
range 0.1<=z<=0.52, (c) classified as clusters in the RBS, (d) not a member of
the Abell catalogue and, finally, (e) visible from the ESO sites La
Silla/Paranal (declination \delta<=20deg). In total we found more than 35
(giant) arc/arclet candidates, including a possible radial arc, one
galaxy-galaxy lensing event and a possible quasar triple image in 14 of the 21
clusters of galaxies. Hence 66% of the sample members are possible lenses.Comment: Accepted for publication in Astronomy and Astrophysics; 8 pages
(excl. Appendix), 6 figures, 9 tables; Please download the high-res images of
the appendix from
http://astro-staff.uibk.ac.at/~w.kausch/ARCRAIDER_II_images.tar.g
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