CONSTRAINT ON THE COSMOLOGICAL CONSTANT FROM GRAVITATIONAL LENSING IN AN EVOLUTIONARY MODEL OF GALAXIES

1998 ◽  
Vol 13 (24) ◽  
pp. 4227-4236 ◽  
Author(s):  
DEEPAK JAIN ◽  
N. PANCHAPAKESAN ◽  
S. MAHAJAN ◽  
V. B. BHATIA
Keyword(s):  
Cosmological Constant ◽  
Galaxy Evolution ◽  
Optical Depth ◽  
Gravitational Lensing ◽  
Statistical Study ◽  
Evolutionary Model ◽  
Building Blocks ◽  
Lens Model ◽  
Gravitational Lenses ◽  
Luminosity Evolution

We study the effect of the cosmological constant on the statistical properties of gravitational lenses in flat cosmologies (Ω0+λ0=1). It is shown that some of the lens observables are strongly affected by the cosmological constant, especially in a low-density universe, and its existence might be inferred by a statistical study of the lenses. In particular, the optical depth of the lens distribution may be used best for this purpose without depending much on the lens model. We calculate the optical depth (probability of a beam encountering a lens event) for a source in a new picture of galaxy evolution based on number evolution in addition to pure luminosity evolution. It seem that present-day galaxies result from the merging of a large number of building blocks. We have tried to put a limit on the cosmological constant in this new picture of galaxy evolution. This evolutionary model of galaxies permits a larger value of the cosmological constant.

scholarly journals CONSTRAINTS ON COSMIC EQUATION OF STATE USING GRAVITATIONAL LENSING STATISTICS WITH EVOLVING GALAXIES

2003 ◽  
Vol 12 (01) ◽  
pp. 101-119 ◽  
Author(s):  
ABHA DEV ◽  
DEEPAK JAIN ◽  
N. PANCHAPAKESAN ◽  
S. MAHAJAN ◽  
V. B. BHATIA
Keyword(s):  
Equation Of State ◽  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Entire Range ◽  
Cosmological Parameters ◽  
Observational Constraints ◽  
Number Density ◽  
Cosmological Observations ◽  
Likelihood Analysis ◽  
Luminosity Evolution

In this paper, observational constraints on the cosmic equation of state of dark energy (p = wρ) have been investigated using gravitational lensing statistics. A likelihood analysis of the lens survey has been carried out to constrain the cosmological parameters Ωmand w. Constraints on Ωmand w are obtained in three different models of galaxy evolution: no evolution model (comoving number density of galaxies remain constant), Volmerange and Guiderdoni Model and fast merging model. The last two models consider the number evolution of galaxies in addition to the luminosity evolution. The likelihood analysis shows that for the no-evolution case w ≤ -0.04 and Ωm≤ 0.90 at 1σ (68% confidence level (CL)). Similarly for the Volmerange & Guiderdoni Model the constraints are w ≤ -0.04 and Ωm≤ 0.91 at 1σ. In fast merging model the constraint become weaker and it allows almost the entire range of parameters. For the case of constant Λ (w = -1), all the models permit Ωm= 0.3 with 68% CL, which is consistent with the value of Ωminferred from various other cosmological observations.

scholarly journals CONSTRAINTS ON GALAXY EVOLUTION THROUGH GRAVITATIONAL LENSING STATISTICS

2000 ◽  
Vol 15 (01) ◽  
pp. 41-53 ◽  
Author(s):  
DEEPAK JAIN ◽  
N. PANCHAPAKESAN ◽  
S. MAHAJAN ◽  
V. B. BHATIA
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Cosmic Time ◽  
Evolutionary Model ◽  
Gravitational Lens ◽  
Observational Cosmology ◽  
Number Density ◽  
Evolution Of Galaxies ◽  
Accretion Model ◽  
Image Separation

Explaining the formation and evolution of galaxies is one of the most challenging problems in observational cosmology. Many observations suggest that galaxies we see today could have evolved from the merging of smaller subsystems. Evolution of galaxies tells us how the mass or number density of the lens varies with cosmic time. Merging between the galaxies and the infall of surrounding mass into galaxies are two possible processes that can change the comoving number density of galaxies and/or their mass. We consider five different evolutionary models of galaxies. These models are: Non-evolutionary model, Guiderdoni and Volmerange model, fast merging, slow merging and mass accretion model. We study the gravitational lens image separation distribution function for these models of evolving galaxies. A comparison with data for lensed quasars taken from the HST snapshot survey rules out the fast merging model completely as this model produces a large number of small-separation lenses. It is possible that the mass accretion model and the non-evolutionary model of galaxies may be able to explain the small angle separations.

Gravitational Lensing as Probe of Large Scale Structure of the Universe

2005 ◽  
Vol 201 ◽  
pp. 437-438
Author(s):  
V. B. Bhatia ◽  
D. Jain ◽  
S. Mahajan ◽  
N. Panchapakesan
Keyword(s):  
Cosmological Constant ◽  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Gamma Ray ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Red Shift ◽  
Sources Of Uncertainty ◽  
The Universe

We apply gravitational lensing statistics to: (1) place a limit on the cosmological constant (ΩΛ); (2) place a limit on the average red-shift (< z >) of gamma-ray bursters (GRBs); (3) investigate models of galaxy evolution to see how compatible these models are with lensing statistics. We also point out the sources of uncertainty in lensing statistics, leading to uncertainty in the results.

Realistic Galaxy Models for Lensing Statistics

2005 ◽  
Vol 201 ◽  
pp. 292-295
Author(s):  
David. Rusin ◽  
Max. Tegmark
Keyword(s):  
Cosmological Constant ◽  
Optical Depth ◽  
Gravitational Lensing ◽  
Significant Progress ◽  
Data Set ◽  
Cosmological Constraints ◽  
Lens Galaxies

The gravitational lensing rate in a well-defined sample of sources can place strong bounds on the cosmological constant, but only if the lensing optical depth is robustly calculated. Significant progress is likely to be achieved by employing more realistic models to describe the population of lens galaxies. Here we investigate the role of elliptical deflectors in lensing statistics, and their effect on cosmological constraints derived from the JVAS survey. We also evaluate the prospects for constraining the cosmological constant using the much larger CLASS data set.

scholarly journals Generalised model-independent characterisation of strong gravitational lenses

2018 ◽  
Vol 620 ◽  
pp. A86 ◽  
Author(s):  
Jenny Wagner
Keyword(s):  
Time Delay ◽  
Gravitational Lensing ◽  
General Class ◽  
Deflection Angle ◽  
Lens Model ◽  
Gravitational Lenses ◽  
Source Position ◽  
Multiple Images ◽  
Model Independent ◽  
The Deflection Angle

Based on the standard gravitational lensing formalism with its effective, projected lensing potential in a given background cosmology, we investigated under which transformations of the source position and of the deflection angle the observable properties of the multiple images remain invariant. These observable properties are time delay differences, the relative image positions, relative shapes, and magnification ratios. As they only constrain local lens properties, we derive general, local invariance transformations in the areas covered by the multiple images. We show that the known global invariance transformations, for example, the mass-sheet transformation or the source position transformation, are contained in our invariance transformations, when they are restricted to the areas covered by the multiple images and when lens-model-based degeneracies are ignored, like the freedom to add or subtract masses in unconstrained regions without multiple images. Hence, we have identified the general class of invariance transformations that can occur, in particular in our model-independent local characterisation of strong gravitational lenses.

scholarly journals A Model-Independent Characterisation of Strong Gravitational Lensing by Observables

Universe ◽  
2019 ◽  
Vol 5 (7) ◽  
pp. 177 ◽  
Author(s):  
Jenny Wagner
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Mass Density ◽  
Model Fitting ◽  
Mass Scale ◽  
Lens Model ◽  
Multiple Images ◽  
Strong Gravitational Lensing ◽  
Consistent Model ◽  
Local Properties

When light from a distant source object, like a galaxy or a supernova, travels towards us, it is deflected by massive objects that lie in its path. When the mass density of the deflecting object exceeds a certain threshold, multiple, highly distorted images of the source are observed. This strong gravitational lensing effect has so far been treated as a model-fitting problem. Using the observed multiple images as constraints yields a self-consistent model of the deflecting mass density and the source object. As several models meet the constraints equally well, we develop a lens characterisation that separates data-based information from model assumptions. The observed multiple images allow us to determine local properties of the deflecting mass distribution on any mass scale from one simple set of equations. Their solution is unique and free of model-dependent degeneracies. The reconstruction of source objects can be performed completely model-independently, enabling us to study galaxy evolution without a lens-model bias. Our approach reduces the lens and source description to its data-based evidence that all models agree upon, simplifies an automated treatment of large datasets, and allows for an extrapolation to a global description resembling model-based descriptions.

scholarly journals Quantifying the structure of strong gravitational lens potentials with uncertainty-aware deep neural networks

2020 ◽  
Vol 499 (4) ◽  
pp. 5641-5652
Author(s):  
Georgios Vernardos ◽  
Grigorios Tsagkatakis ◽  
Yannis Pantazis
Keyword(s):  
Confidence Intervals ◽  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Probability Distributions ◽  
Mass Density ◽  
Ground Truth ◽  
Gaussian Random Fields ◽  
Training Data ◽  
Gravitational Lens ◽  
Data Set

ABSTRACT Gravitational lensing is a powerful tool for constraining substructure in the mass distribution of galaxies, be it from the presence of dark matter sub-haloes or due to physical mechanisms affecting the baryons throughout galaxy evolution. Such substructure is hard to model and is either ignored by traditional, smooth modelling, approaches, or treated as well-localized massive perturbers. In this work, we propose a deep learning approach to quantify the statistical properties of such perturbations directly from images, where only the extended lensed source features within a mask are considered, without the need of any lens modelling. Our training data consist of mock lensed images assuming perturbing Gaussian Random Fields permeating the smooth overall lens potential, and, for the first time, using images of real galaxies as the lensed source. We employ a novel deep neural network that can handle arbitrary uncertainty intervals associated with the training data set labels as input, provides probability distributions as output, and adopts a composite loss function. The method succeeds not only in accurately estimating the actual parameter values, but also reduces the predicted confidence intervals by 10 per cent in an unsupervised manner, i.e. without having access to the actual ground truth values. Our results are invariant to the inherent degeneracy between mass perturbations in the lens and complex brightness profiles for the source. Hence, we can quantitatively and robustly quantify the smoothness of the mass density of thousands of lenses, including confidence intervals, and provide a consistent ranking for follow-up science.

scholarly journals Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen

1996 ◽  
Vol 173 ◽  
pp. 97-98
Author(s):  
Matthias Bartelmann ◽  
Abraham Loeb
Keyword(s):  
Observational Data ◽  
Gravitational Lensing ◽  
Column Density ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Absorption Lines ◽  
Gravitational Lenses ◽  
High Column

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.

scholarly journals Poor Groups Around Strong Gravitational Lenses

2006 ◽  
Vol 2 (S235) ◽  
pp. 230-230
Author(s):  
Ivelina Momcheva ◽  
Kurtis Williams ◽  
Ann Zabludoff ◽  
Charles Keeton
Keyword(s):  
Galaxy Evolution ◽  
Velocity Dispersion ◽  
Gravitational Lenses ◽  
Local Universe ◽  
Groups Of Galaxies ◽  
Hot Gas ◽  
Gas Kinematics ◽  
The Galaxy ◽  
Group Centroid ◽  
Group Galaxy

AbstractPoor groups are common and interactive environments for galaxies, and thus are important laboratories for studying galaxy evolution. Unfortunately, little is known about groups at z ≥ 0.1, because of the difficulty in identifying them in the first place. Here we present results from our ongoing survey of the environments of strong gravitational lenses, in which we have so far discovered six distant (z ≥ 0.5) groups of galaxies. As in the local Universe, the highest velocity dispersion groups contain a brightest member spatially coincident with the group centroid, whereas lower-dispersion groups tend to have an offset brightest group galaxy. This suggests that higher-dispersion groups are more dynamically relaxed than lower-dispersion groups and that at least some evolved groups exist by z ~ 0.5. We also compare the galaxy and hot gas kinematics with those of similarly distant clusters and of nearby groups.

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