16,379 research outputs found
Weak Gravitational Lensing by Dark Clusters
We calculate the abundance of dark-matter concentrations that are
sufficiently overdense to produce a detectable weak-gravitational-lensing
signal. Most of these overdensities are virialized halos containing
identifiable X-ray and/or optical clusters. However, a significant fraction are
nonvirialized overdensities still in the process of gravitational
collapse--these should produce significantly weaker or no X-ray emission. Our
predicted abundance of such dark clusters are consistent with the abundance
implied by the Erben et al. (2000) detection of a dark lens. Weak lensing by
these nonvirialized objects will need to be considered when determining
cosmological parameters with the lens abundance in future weak-lensing surveys.
Such weak lenses should also help shed light on the process of cluster
formation.Comment: 18 pages, 11 figures; a few sentences and a figure added, conclusions
unchanged, published in MNRA
Probing Galaxy Dark Matter Haloes in COSMOS with Weak Lensing Flexion
Current theories of structure formation predict specific density profiles of
galaxy dark matter haloes, and with weak gravitational lensing we can probe
these profiles on several scales. On small scales, higher-order shape
distortions known as flexion add significant detail to the weak lensing
measurements. We present here the first detection of a galaxy-galaxy flexion
signal in space-based data, obtained using a new Shapelets pipeline introduced
here. We combine this higher-order lensing signal with shear to constrain the
average density profile of the galaxy lenses in the Hubble Space Telescope
COSMOS survey. We also show that light from nearby bright objects can
significantly affect flexion measurements. After correcting for the influence
of lens light, we show that the inclusion of flexion provides tighter
constraints on density profiles than does shear alone. Finally we find an
average density profile consistent with an isothermal sphere.Comment: 14 pages, 14 figures. Accepted for publication in MNRA
Probing the Universe with Weak Lensing
Gravitational lenses can provide crucial information on the geometry of the
Universe, on the cosmological scenario of formation of its structures as well
as on the history of its components with look-back time. In this review, I
focus on the most recent results obtained during the last five years from the
analysis of the weak lensing regime. The interest of weak lensing as a probe of
dark matter and the for study of the coupling between light and mass on scales
of clusters of galaxies, large scale structures and galaxies is discussed
first. Then I present the impact of weak lensing for the study of distant
galaxies and of the population of lensed sources as function of redshift.
Finally, I discuss the potential interest of weak lensing to constrain the
cosmological parameters, either from pure geometrical effects observed in
peculiar lenses, or from the coupling of weak lensing with the CMB.Comment: To appear Annual Review of Astronomy and Astrophysiscs Vol. 37. Latex
and psfig.sty. Version without figure, 54 pages, 73Kb. Complete version
including 13 figures (60 pages) available on ftp.iap.fr anonymous account in
/pub/from_users/mellier/AnnualReview ; file ARAAmellier.ps.gz 1.6 M
Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales
Most of the matter in the universe is not luminous and can be observed
directly only through its gravitational effect. An emerging technique called
weak gravitational lensing uses background galaxies to reveal the foreground
dark matter distribution on large scales. Light from very distant galaxies
travels to us through many intervening overdensities which gravitationally
distort their apparent shapes. The observed ellipticity pattern of these
distant galaxies thus encodes information about the large-scale structure of
the universe, but attempts to measure this effect have been inconclusive due to
systematic errors. We report the first detection of this ``cosmic shear'' using
145,000 background galaxies to reveal the dark matter distribution on angular
scales up to half a degree in three separate lines of sight. The observed
angular dependence of this effect is consistent with that predicted by two
leading cosmological models, providing new and independent support for these
models.Comment: 18 pages, 5 figures: To appear in Nature. (This replacement fixes tex
errors and typos.
Disentangling dark sector models using weak lensing statistics
We perform multi-plane ray-tracing using the GLAMER gravitational lensing
code within high-resolution light-cones extracted from the CoDECS simulations:
a suite of cosmological runs featuring a coupling between Dark Energy and Cold
Dark Matter. We show that the presence of the coupling is evident not only in
the redshift evolution of the normalisation of the convergence power spectrum,
but also in differences in non-linear structure formation with respect to
{\Lambda}CDM. Using a tomographic approach under the assumption of a
{\Lambda}CDM cosmology, we demonstrate that weak lensing measurements would
result in a {\sigma}8 value that changes with the source redshift if the true
underlying cosmology is a coupled Dark Energy one. This provides a generic null
test for these types of models. We also find that different models of coupled
Dark Energy can show either an enhanced or a suppressed correlation between
convergence maps with differing source redshifts as compared to {\Lambda}CDM.
This would provide a direct way to discriminate between different possible
realisations of the coupled Dark Energy scenario. Finally, we discuss the
impact of the coupling on several lensing observables for different source
redshifts and angular scales with realistic source redshift distributions for
current ground-based and future space-based lensing surveys.Comment: 17 pag. and 14 fig. replaced to match the accepted version (increased
the number of light-cone realisations
Constraints on non-thermal Dark Matter from Planck lensing extraction
Distortions of CMB temperature and polarization anisotropy maps caused by
gravitational lensing, observable with high angular resolution and sensitivity,
can be used to constrain the sterile neutrino mass, offering several advantages
against the analysis based on the combination of CMB, LSS and Ly\alpha forest
power spectra. As the gravitational lensing effect depends on the matter
distribution, no assumption on light-to-mass bias is required. In addition,
unlike the galaxy clustering and Ly\alpha forest power spectra, the projected
gravitational potential power spectrum probes a larger range of angular scales,
the non-linear corrections being required only at very small scales. Taking
into account the changes in the time-temperature relation of the primordial
plasma and the modification of the neutrino thermal potential, we compute the
projected gravitational potential power spectrum and its correlation with the
temperature in the presence of DM sterile neutrino. We show that the
cosmological parameters are generally not biased when DM sterile neutrino is
included. From this analysis we found a lower limit on DM sterile neutrino mass
m_s >2.08 keV at 95% CL, consistent with the lower mass limit obtained from the
combined analysis of CMB, SDSS 3D power spectrum and SDSS Ly\alpha forest power
spectrum ( keV). We conclude that although the information that
can be obtained from lensing extraction is rather limited due to the high level
of the lensing noise of Planck experiment, weak lensing of CMB offers a
valuable alternative to constrain the dark matter sterile neutrino mass.Comment: 15 pages, 6 figure
Superfluid dark matter in tension with weak gravitational lensing data
Superfluid dark matter (SFDM) is a model that promises to reproduce the
successes of both particle dark matter on cosmological scales and those of
Modified Newtonian Dynamics (MOND) on galactic scales. SFDM reproduces MOND
only up to a certain distance from the galactic center, and only for kinematic
observables: It does not affect trajectories of light. We test whether this is
consistent with a recent analysis of weak gravitational lensing that has probed
accelerations around galaxies to unprecedentedly large radii. This analysis
found the data to be close to the prediction of MOND, suggesting they might be
difficult to fit with SFDM. To investigate this matter, we solved the equations
of motion of the model and compared the result to observational data. Our
results show that the SFDM model is incompatible with the weak-lensing
observations, at least in its current form.Comment: 20 pages, 12 figure
The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B
We have identified a merging galaxy cluster with evidence of two distinct
sub-clusters. The X-ray and optical data suggest that the subclusters are
moving away from each other after closest approach. This cluster merger was
discovered from observations of the well localized short-duration gamma-ray
burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position
is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent
Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB
coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the
cluster. Deep multi-epoch optical images were obtained to constrain the
evolution of the GRB afterglow, including a 27480s exposure in the F814W band
with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the
deepest imaging ever obtained towards a known galaxy cluster in a single
passband. We perform a weak gravitational lensing analysis, including mapping
the total mass distribution of the merger system. Combined with Chandra X-ray
Observatory and Swift/XRT observations, we investigate the dynamical state of
the merger to probe the nature of the dark matter component. Our weak
gravitational lensing measurements reveal a separation of the X-ray centroid of
the western subcluster from the center of the mass and galaxy light
distributions, similar to that of the famous "Bullet cluster". We conclude that
the "Burst cluster" is another candidate merger system for determining the
nature of dark matter and for studying the environment of short GRBs. We
discuss connections between the cluster dynamical state and/or matter
composition and compact object mergers, the leading model for the origin of
short GRBs. Finally, we present results from a weak lensing survey based on
archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.Comment: 17 pages, 7 figures, accepted by Ap
Intrinsic Correlation of Galaxy Shapes: Implications for Weak Lensing Measurements
Weak gravitational lensing is now established as a powerful method to measure
mass fluctuations in the universe. It relies on the measurement of small
coherent distortions of the images of background galaxies. Even low-level
correlations in the intrinsic shapes of galaxies could however produce a
significant spurious lensing signal. These correlations are also interesting in
their own right, since their detection would constrain models of galaxy
formation. Using halos found in N-body simulations, we
compute the correlation functions of the intrinsic ellipticity of spiral
galaxies assuming that the disk is perpendicular to the angular momentum of the
dark matter halo. We also consider a simple model for elliptical galaxies, in
which the shape of the dark matter halo is assumed to be the same as that of
the light. For deep lensing surveys with median redshifts , we find
that intrinsic correlations of on angular scales are generally below the expected lensing signal, and contribute only a
small fraction of the excess signals reported on these scales. On larger scales
we find limits to the intrinsic correlation function at a level ,
which gives a (model-dependent) range of separations for which the intrinsic
signal is about an order of magnitude below the ellipticity correlation
function expected from weak lensing. Intrinsic correlations are thus negligible
on these scales for dedicated weak lensing surveys. For wider but shallower
surveys such as SuperCOSMOS, APM and SDSS, we cannot exclude the possibility
that intrinsic correlations could dominate the lensing signal. We discuss how
such surveys could be used to calibrate the importance of this effect, as well
as study spin-spin correlations of spiral galaxies.Comment: 7 pages, 8 figures. Version accepted by MNRA
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