826 research outputs found

### The Redshift Distribution of Distant Sources from Gravitational Depletion in Clusters

Gravitational lensing can be used to analyze the redshift distribution of
faint galaxies. In particular the magnification bias modifies locally the
galaxy number density of lensed sources observed in lensing clusters. This
depletion area probes the redshift distribution of galaxies beyond B=25. In
this proceeding I present this new tool to infer the redhsift distribution of
faint galaxies.Comment: To appear in "The Young Universe". Ed. S. D'Odorico, A. Fontana & E.
Giallongo, ASP Conf. Ser. Latex with paspconf.sty and psfig.sty. 4 pages, 2
figures. 43. Kb gzipped tar fil

### Weak Lensing as a Probe of Dark Matter

Weak gravitational lensing of distant galaxies can probe the total projected
mass distribution of foreground gravitational structures on all scales and has
been used successfully to map the projected mass distribution of rich
intermediate redshift clusters. This paper reviews the general concepts of the
lensing analysis. We focus on the relation between the observable (shapes and
fluxes) and physical (mass, redshift) quantities and discuss some observational
issues and recent developments on data analysis which appear promising for a
better measurement of the lensing signatures (distortion and magnification) at
very large scales.Comment: 8 pages, Latex with 2 included postscript figures, 1 55kB JPEG figure
(also available as (1.1MB) compressed ps file from anonymous ftp at
ftp://summer.obs-mip.fr/pub/OUTGOING/ludo/simul.ps.Z), to be published in the
proceedings of the XXXIst Rencontres de Moriond, Les Arcs, France, January
20-27 199

### Gravitational Lensing by Large Scale Structures: A Review

We review all the cosmic shear results obtained so far, with a critical
discussion of the present strengths and weaknesses. We discuss the future
prospects and the role cosmic shear could play in a precision cosmology era.Comment: 48 pages, Lecture given at the Aussois winter school, january 200

### High Resolution Data on the Cloverleaf in the UV and in CO(7-6)

We present a new investigation of the Cloverleaf (z$=$2.56) based on the
HST/WFPC2, IRAM and CFHT/FOCAM images data. The WFPC2 data shows a significant
overdensity of galaxies around the Cloverleaf that we interpret as the presence
of a distant cluster of galaxies along the line of sight. The Cloverleaf is
probably the result of the lensing effects which include, in addition to a
single galaxy, a distant clusters of galaxies. We have modelled the lens
accordingly. The high-resolution IRAM/CO map provides the orientation and the
ellipticity of the CO spots induced by the shear component. Velocity-positional
effects are detected at the 8$\sigma$ level in the CO map. A strong limit can
then be put on the size, shape and location of the CO source around the quasar.
The CO source is found to form a disk- or ring- structure orbiting the
central engine at $\sim$ 100km/s at a radial distance of $\sim$ 100pc, leading
to a central mass of $\sim$ 10$^{9}$ M$_\odot$ possibly in the form of a black
hole.Comment: To appear in "Molecular Lines at High Redshift". Greenbank Oct. 97.
C. Arilli, S. Radford, K. Menten eds. Latex with paspconf.sty and psfig.sty.
7 pages, 3 figures only available on ftp.iap.fr: /pub/from_users/mellier/
alloind_fig.tar.gz (486 Kb). 25 Kb gzipped tar fil

### Dark Matter and Gravitational Lensing

The last decade has shown a considerable development of gravitational lensing
for cosmology because it probes the amount and the nature of dark matter, and
provides information on the density parameter $\Omega$, the cosmological
constant $\Lambda$ and the Hubble constant $H_{o}$. Therefore, gravitational
lensing can constrain the cosmological scenario which gave birth to the
Universe as it appears today. The ongoing programs and future projects which
are developing now all over the world show that gravitational lensing is
considered as a major cosmological tool for the coming years as well. In this
review, we summarize some of the most recent advances in the fields relevant
for the dark matter issue. We will focus on the microlensing, the arc(let)s and
the weak lensing studies. The possibility to check the existence of a non-zero
$\Lambda$ is presented elsewhere.Comment: To appear in the "IVieme colloque de cosmologie". June 4-6 1997,
Observatoire de Paris. Latex with sprocl.sty and psfig.sty. 14 pages, 3
figures. Fig. 2 and 3 only available on ftp.iap.fr : /pub/from_users/mellier/
(simul.lss.ps=23.6 Kb and panelarc.ps=1.5 Mb). 28.5 Kb gzipped tar fil

### Cosmic Shear: The Dark Side of the Universe

We discuss the present status and future prospects for cosmic shear
observations and their cosmological constraints. We review the evidences
supporting the cosmological origin of the measured signal, and discuss the
possible problems coming from intrinsic alignment and from the actual
limitations of theoretical predictions.Comment: 6 pages, Cosmic shear review, To appear in the Proceedings of the
XXXVIIth Moriond Astrophysics Meeting "The Cosmological Model

### Efficiency of weak lensing surveys to probe cosmological models

We apply a mass reconstruction technique to simulated large-scale structure
gravitational distortion maps, from 2.5' to 10 degree scales, for different
cosmological scenarii. The projected mass is reconstructed using a
non-parametric least square method after noise due to the galaxy intrinsic
ellipticities has been added on. The shearing of the galaxies is performed
using the full lensing equation, without any hypothesis like the weak lensing
approximation, or other linearization. It is shown that, in the reconstructed
maps the noise acts as a perfect uncorrelated Poisson noise, with no
propagation at large scales. The measured power spectrum and first four moments
of the convergence can be corrected accurately for this source of noise. Using
60 realizations for each model, we show that a weak lensing survey of 5x5
degrees with a typical sheared background population of 30 gal/arcmin^2 at a
redshift z_s=1, is able to probe the amplitude of the power spectrum with a few
percents accuracy. Such a survey would lead to a 6 sigma separation between
open (Omega=0.3) and flat (Omega=1) model. This separation is shown to be
robust against different hypothesis for the normalization or the shape of the
power spectrum, and does not require very deep surveys. The observational
strategy for an optimal measurement of the power spectrum and the moments of
the convergence is discussed.Comment: 22 pages, latex. Replaced by the accepted version, A&A in pres

### The X-ray Morphology of the Lensing Galaxy Cluster Cl0024+17

The paper reports the analysis of a very deep ROSAT HRI observation of the
distant lensing cluster, CL0024+17. The morphology of the cluster is studied
and the small core radius inferred from lensing analysis is confirmed.
Constraints on the mass distribution are discussed.Comment: 8 pages, 4 figures, Astronomy & Astrophysics in pres

### Gravitational Lensing and the Redshift Distribution of $B>25$ galaxies

In addition to the determination of the mass distribution of lenses (see P.
Schneider, this conference), strong and weak lensing can also be powerfull
tools to analyse the redshift distribution of faint galaxies. In this review, I
summarize the present status of redshifts of galaxies beyond $B=25$ as they are
inferred by spectroscopy of magnified galaxies, lensing inversion and
magnification bias.Comment: 8 pages, Invited talks for the 37th Herstmonceux Conference on "HST
and the High Redshift Universe" 1-5 july 1996. Latex with hx37_latex.sty and
psfig.sty. 8 pages, 4 figures 191K gzipped tar file. Also available on
ftp.iap.fr/pub/incoming/mellie

### Weak Lensing Statistics as a Probe of Omega and Power Spectrum

The possibility of detecting weak lensing effects from deep wide field
imaging surveys has open new means of probing the large-scale structures of the
Universe and measuring cosmological parameters. In this paper we present a
systematic study of the expected dependence of the low order moments of the
filtered gravitational local convergence with the power spectrum of the density
fluctuations and with the cosmological parameters Omega_0 and Lambda. The
results show a significant dependence with all these parameters. Though we note
that this degeneracy could be partially raised by considering two populations
of sources, at different redshifts, computing the third moment is more
promising since it is expected, in the quasi-linear regime and for Gaussian
initial conditions, to be only $\Omega_0$ dependent (with a slight degeneracy
with Lambda) when it is correctly expressed in terms of the second moment.
More precisely we show that the variance of the convergence varies
approximately as P(k) Omega_0^{1.5} z_s^{1.5}, whereas the skewness varies as
Omega_0^{-0.8} z_s^{-1.35}, where P(k) is the projected power spectrum and z_s
the redshift of sources. Thus, used jointly they can provide both P(k) and
Omega_0. However, the dependence with the redshift of sources is large and
could be a major concern for a practical implementation.
We have estimated the errors expected for these parameters in realistic
scenario and sketched what would be the observational requirements for doing
such measurements. A more detailed study of an observational strategy is left
for a second paper.Comment: 19 pages, 12 figures, LaTeX, published in Astronomy and Astrophysics
1997, 322,

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