1,229 research outputs found
Searching dark-matter halos in the GaBoDS survey
We apply the linear filter for the weak-lensing signal of dark-matter halos
developed in Maturi et al. (2005) to the cosmic-shear data extracted from the
Garching-Bonn-Deep-Survey (GaBoDS). We wish to search for dark-matter halos
through weak-lensing signatures which are significantly above the random and
systematic noise level caused by intervening large-scale structures. We employ
a linear matched filter which maximises the signal-to-noise ratio by minimising
the number of spurious detections caused by the superposition of large-scale
structures (LSS). This is achieved by suppressing those spatial frequencies
dominated by the LSS contamination. We confirm the improved stability and
reliability of the detections achieved with our new filter compared to the
commonly-used aperture mass (Schneider, 1996; Schneider et al., 1998) and to
the aperture mass based on the shear profile expected for NFW haloes (see e.g.
Schirmer et al., 2004; Hennawi & Spergel, 2005). Schirmer et al.~(2006)
achieved results comparable to our filter, but probably only because of the low
average redshift of the background sources in GaBoDS, which keeps the LSS
contamination low. For deeper data, the difference will be more important, as
shown by Maturi et al. (2005). We detect fourteen halos on about eighteen
square degrees selected from the survey. Five are known clusters, two are
associated with over-densities of galaxies visible in the GaBoDS image, and
seven have no known optical or X-ray counterparts.Comment: 8 pages, 4 figures, accepted by A&
Searching for galaxy clusters using the aperture mass statistics in 50 VLT fields
Application of the aperture mass (Map-) statistics provides a weak lensing
method for the detection of cluster-sized dark matter halos. We present a new
aperture filter function and maximise the effectiveness of the Map-statistics
to detect cluster-sized halos using analytical models. We then use weak lensing
mock catalogues generated from ray-tracing through N-body simulations, to
analyse the effect of image treatment on the expected number density of halos.
Using the Map-statistics, the aperture radius is typically several arcminutes,
hence the aperture often lies partly outside a data field, consequently the
signal-to-noise ratio of a halo detection decreases. We study these border
effects analytically and by using mock catalogues. We find that the expected
number density of halos decreases by a factor of two if the size of a field is
comparable to the diameter of the aperture used. We finally report on the
results of a weak lensing cluster search applying the Map-statistics to 50
randomly selected fields which were observed with FORS1 at the VLT. Altogether
the 50 VLT fields cover an area of 0.64 square degrees. The I-band images were
taken under excellent seeing conditions (average seeing 0.6 arcsec.) which
results in a high number density of galaxies used for the weak lensing analysis
(26/sq.arcmin). In five of the VLT fields, we detect a significant Map-signal
which coincides with an overdensity of the light distribution. These detections
are thus excellent candidates for shear-selected clusters.Comment: 23 pages, 5 tables, 24 figures, published in A&A, Sect. 3.5 and 7 are
changed or altered; Fig. 11 is change
The Garching-Bonn Deep Survey (GaBoDS) Wide-Field-Imaging Reduction Pipeline
We introduce our publicly available Wide-Field-Imaging reduction pipeline
THELI. The procedures applied for the efficient pre-reduction and astrometric
calibration are presented. A special emphasis is put on the methods applied to
the photometric calibration. As a test case the reduction of optical data from
the ESO Deep Public Survey including the WFI-GOODS data is described. The
end-products of this project are now available via the ESO archive Advanced
Data Products section.Comment: 6 pages, 3 figures, proceedings of ESO Calibration Workshop 200
Beyond the pale?: the implications of the RSLG Report for non-CURL modern university libraries: Perspectives on the support libraries group: Final report
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
An optimal filter for the detection of galaxy clusters through weak lensing
We construct a linear filter optimised for detecting dark-matter halos in
weak-lensing data. The filter assumes a mean radial profile of the halo shear
pattern and modifies that shape by the noise power spectrum. Aiming at
separating dark-matter halos from spurious peaks caused by large-scale
structure lensing, we model the noise as being composed of weak lensing by
large-scale structures and Poisson noise from random galaxy positions and
intrinsic ellipticities. Optimal filtering against the noise requires the
optimal filter scale to be smaller than typical halo sizes. Although a perfect
separation of halos from spurious large-scale structure peaks is strictly
impossible, we use numerical simulations to demonstrate that our filter
produces substantially more sensitive, reliable and stable results than the
conventionally used aperture-mass statistic.Comment: 9 pages, 6 figures, A&A submitte
GaBoDS: The Garching-Bonn Deep Survey -- II. Confirmation of EIS cluster candidates by weak gravitational lensing
We report the first confirmation of colour-selected galaxy cluster candidates
by means of weak gravitational lensing. Significant lensing signals were
identified in the course of the shear-selection programme of dark matter haloes
in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of
deep, high-quality imaging data on the southern sky. The detection was made in
a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A
highly significant shear-selected mass-concentration perfectly coincides with
the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature.
Several other shear patterns in the field can also be identified with cluster
candidates, one of which could possibly be part of a filament at z~0.45.Comment: 4 pages, 4 figures, submitted to A&A Letter
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&
Mass, Light and Colour of the Cosmic Web in the Supercluster SCL2243-0935 (z=0.447)
Context: In 2.2m MPG-ESO/WFI data we discovered several mass peaks through
weak lensing, forming a possible supercluster at redshift 0.45. Through
multi-colour wide-field imaging with CFHT/Megaprime and INT/WFC we identify
early-type galaxies and trace the supercluster network with them. Through
EMMI/NTT multi-object spectroscopy we verify the initial shear-selected cluster
candidates. Using weak lensing we obtain mass estimates for the supercluster
centre and the filaments.
Results: We identified the centre of the SCL2243-0935 supercluster, MACS
J2243-0935, which was found independently by Ebeling et al. (2010). 13 more
clusters or overdensities are embedded in a filamentary network, half of them
are already spectroscopically confirmed. Three (5-15) Mpc filaments are
detected, and we estimate the global size of SCL2243 to 45x15x50 Mpc, making it
one of the largest superclusters known at intermediate redshifts. Weak lensing
yields r_200=(2.06+/-0.13) Mpc and M_200=(1.54+/-0.29)x10^15 M_sun for MACS
J2243 with M/L=428+/-82, very similar to results from size-richness cluster
scaling relations. Integrating the weak lensing surface mass density over the
supercluster network (defined by increased i-band luminosity or g-i colours),
we find (1.53+/-1.01)x10^15 M_sun and M/L=305+/-201 for the three main
filaments, consistant with theoretical predictions. The filaments' projected
surface mass density is 0.007-0.012, corresponding to 10-100 times the critical
density. The greatly varying density of the cosmic web is also reflected in the
mean colour of galaxies. Conclusions: SCL2243 is significantly larger and much
more richly structured than other known superclusters such as A901/902 or
MS0302 studied with weak lensing before. It is a text-book supercluster with
little contamination along the line of sight, making it a perfect sandbox for
testing new techniques probing the cosmic web.Comment: 26 pages, 16 figures, accepted for publication Astronomy and
Astrophysics. Minor corrections implemented as requested by the refere
Mass-detection of a matter concentration projected near the cluster Abell 1942: Dark clump or high-redshift cluster?
A weak-lensing analysis of wide-field - and -band images centered on
the cluster Abell 1942 has uncovered a mass concentration arcminutes
South of the cluster center. A statistical analysis shows that the detections
are highly significant. No strong concentration of bright galaxies is seen at
the position of the mass concentration, though a slight galaxy number
overdensity and a weak extended X-ray source are present about 1' away from its
center.
From the spatial dependence of the tangential alignment around the center of
the mass concentration, we inferred a lower bound on the mass inside a sphere
of radius \ts Mpc of , much higher
than crude mass estimates based on X-ray data. No firm conclusion can be
inferred about the nature of the clump. If it were a high-redshift cluster, the
weak X-ray flux would indicate that it had an untypically low X-ray luminosity
for its mass; if the X-ray emission were physically unrelated to the mass
concentration, this conclusion would be even stronger.
The search for massive halos by weak lensing enables us for the first time to
select halos based on their mass properties only and to detect new types of
objects, e.g., dark halos. The mass concentration in the field of A1942 may be
the first example of such a halo.Comment: Sumitted to A&A Main Journal. 15 pages, 11 figures. 75 Kb gzipped tar
file. Figures with images not included, but available on ftp.iap.fr
/pub/from_users/mellier/A1942: a1942darkclump.ps.gz (2.1 Mb
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