69 research outputs found
A radial mass profile analysis of the lensing cluster MS2137-23
We reanalyze the strong lens modeling of the cluster of galaxies MS2137-23
using a new data set obtained with the ESO VLT. We found the photometric
redshifts of the two main arc systems are both at z=1.6. After subtraction of
the central cD star light of the HST image we found that only one object lying
underneath has the expected properties of the fifth image associated to the
tangential arc. We improve the previous lens modelings of the central dark
matter distribution of the cluster, using an isothermal model with a core (IS)
and the NFW-like model with a cusp. Without the fifth image, the arc properties
together with the shear map profile are equally well fit by the and by an IS
and a sub-class of generalized-NFW mass profiles having inner slope power index
in the range 0.7<alpha<1.2. Adding new constrains provided by the fifth image
favors IS profiles that better predict the fifth image properties. A model
including cluster galaxy perturbations or the the stellar mass distribution
does not change our conclusions but imposes the M/L_I of the cD stellar
component is below 10 at a 99% confidence level.
Using our new detailed lensing model together with Chandra X-ray data and the
cD stellar component we finally discuss intrinsic properties of the
gravitational potential. Whereas X-ray and dark matter have a similar shape at
various radius, the cD stellar isophotes are twisted by 13 deg. The sub-
arc-second azimuthal shift we observe between the radial arc position and the
predictions of elliptical models correspond to what is expected from a mass
distribution twist. This shift may result from a projection effect of the cD
and the cluster halos, thus revealing the triaxiality of the system.Comment: Final version accepted in A&
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
Properties of high-z galaxies as seen through lensing clusters
We discuss the first results obtained on the study of a sample of high-z
galaxies (2 < z < 7), using the gravitational amplification effect in the core
of lensing clusters. Sources are located close to the critical lines in
clusters with well constrained mass distributions, and selected through
photometric redshifts, computed on a large wavelength domain, and lens
inversion techniques.Comment: 5 pages, 3 figures, Conference Proceedings of the "Clustering at High
Redshift" Conference, June 29 to July 2, 1999, Marseille (France
Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structures
We report the detection of a significant (5.5 sigma) excess of correlations
between galaxy ellipticities at scales ranging from 0.5 to 3.5 arc-minutes.
This detection of a gravitational lensing signal by large-scale structure was
made using a composite high quality imaging survey of 6300 arcmin^2 obtained at
the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic
CCD cameras. The amplitude of the excess correlation is 2.2\pm 0.2 % at 1
arcmin scale, in agreement with theoretical predictions of the lensing effect
induced by large-scale structure.We provide a quantitative analysis of
systematics which could contribute to the signal and show that the net effect
is small and can be corrected for. We show that the measured ellipticity
correlations behave as expected for a gravitational shear signal. The
relatively small size of our survey precludes tight constraints on cosmological
models. However the data are in favor of cluster normalized cosmological
models, and marginally reject Cold Dark Matter models with (Omega=0.3,
sigma_8<0.6) or (Omega=1, sigma_8=1). The detection of cosmic shear
demonstrates the technical feasibility of using weak lensing surveys to measure
dark matter clustering and the potential for cosmological parameter
measurements, in particular with upcoming wide field CCD cameras.Comment: 19 pages. 19 Figures. Revised version accepted in A&
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