Strong lensing is an effective way to probing the properties of dark energy. In this paper, we use the strong lensing data to constrain the
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) theory, which is a new modified gravity to explain ...the present accelerating cosmic expansion without the need of dark energy. In our discussion, the CMB and BAO data are also added to constrain model parameters tightly and three different
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) models are studied. We find that strong lensing has an important role on constraining
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) models, and once the CMB+BAO data is added, a tighter constraint is obtained. However, the consistency of our result with what is obtained from SNIa+CMB+BAO is actually model-dependent.
The properties of the relativistic rings which show up in images of a source when a black hole lies between the source and observer are examined. The impact parameters are calculated, along with the ...distances of closest approach of the rays which form a relativistic ring, their angular sizes, and their “magnification” factors, which are much less than unity.
Analysis of strong gravitational lensing depends on software analysis of observational data. The purpose of this study is to evaluate the behavior of strong gravitational lens modeling software with ...changes in redshift. Four different strong gravitational lens software modeling codes are directly compared (Lenstool/glafic, two light traces mass codes, and GRALE/PixeLens, two non-light traces mass codes) in the analysis of a mock model as well as analysis of SDSSJ1004 + 4112. The calculated time delay is proportional to DdDs/Dds. The percent change in time delays calculated at each redshift tested is compared with percent change in DdDs/Dds. A mock model with a singular isothermal ellipsoid and four images is tested with each code. Five models are used with a constant zlens and a varying zsource, and five models with a constant zsource and a varying zlens. The effects of changing geometry are similarly investigated for SDSSJ1004 + 4112. In general, the changes in time delay are of a similar magnitude and direction, although some calculated time delays did not follow changes in DdDs/Dds. This variation is explained by changes in image position calculated by glafic and GRALE, which varied according to Dds/Ds. Changes in enclosed mass for the mock model with a constant zsource are similar to changes in DdDs/Dds for three of the four codes tested. These data demonstrate the effect of changes in redshift on parameters calculated by each of the codes as compared to changes in DdDs/Dds. The paucity of comparative studies in strong gravitational lensing suggests the need for further studies. These results show that small changes in redshift affect the calculated time delay and mass, and that the effect on the calculations is dependent on the particular software used.
Les amas de galaxies sont des structures massives composées à plus de 80% de matière noire. Leur coeur peut atteindre une densité de masse critique qui en déformant l'espace-temps fait converger les ...rayons lumineux vers l'observateur. Grâce à des relevés photométriques profonds de l'amas Abell 2744, de nombreux systèmes multiples ont été découverts. Identifier ces systèmes reste un défi, j'ai donc développé une méthode robuste basée sur les propriétés photométriques conservées par l'effet de lentille gravitationnelle qui permet de les détecter automatiquement. Le meilleur moyen de prouver que des images proviennent de la même galaxie reste la mesure de leur distance(redshifts) grâce à leur spectre. En analysant les données collectées par le spectrographe à intégrale de champ MUSE j'ai mesuré un grand nombre de sources (514) dont 83 d'entre elles sont des images multiples. Bénéficiant de cette large couverture spectrale, j'ai créé un modèle paramétrique de masse parmi les plus contraints à ce jour. La sensibilité atteinte par le modèle permet de sonder l'influence de structures périphériques (jusqu'à une distance de 700kpc), révélant ainsi des erreurs systématiques sur la mesure de la masse due à la paramétrisation du modèle (6%). Comparé aux précédentes études, on voit une diminution de 10% de la masse dans un rayon 100 kpc montrant ainsi en partie le gain offert par la spectroscopie. Ce gain, bien que négligeable sur la mesure de l'amplification, s'est avéré pouvoir contraindre la balance en masse entre les différentes composantes de notre modèle, dépassant par endroits 2 fois l'incertitude statistique
Clusters of galaxies are large and massive structures containing more than 80% of dark matter. In the cluster core, the mass density can reach a critical threshold making the curvature of space-time large enough to bend light path and then allow multiple convergence of images from the same sources to appear on the observer field of view. Thanks to deep photometric coverage of Abell 2744, a lot of multiply-imaged systems were discovered. Nevertheless, finding them remain a challenge and based on the preserved photometric properties by lensing, I developed a robust method to automatically find them. However, measuring the redshifts for each multiple images remains the best way to surely associate them. The deep coverage of the integral field spectrograph MUSE allowed me to identify a large number of sources ( 514 ) among them 83 were multiple images. Thanks to this large spectroscopic coverage, I built one of the most constrained parametric mass model for lensing cluster to date. The sensitivity raised by this model allow me to probe the influence of outskirts substructures ( at 700 kpc distance ), revealing systematic sources of uncertainties related to the mass model parametrisation ( 6% ). Compared to previous studies, I notice a 10% lower mass in the center ( within 100kpc ) showing one of the benefit of large spectroscopic constraints. This benefit, is smaller on the amplification estimation but shows a significant discrepancy between different mass counterparts in the models, up to 2 times the statistical uncertainties
This work is focused on a search for strong gravitational lenses in early-type galaxies (ETGs). The total number of samples is 4,706 galaxies encompassing a magnitude range 15.0 < i < 18.0 and colour ...3.5 < (u-r) < 5.0. Two databases were employed as the source of K-band images (UKIDSS Large Area Survey) and g, r, i images (SDSS). All samples were fitted to a Sersic component and automatically processed using GALFIT (Peng et al. 2002; Peng et al. 2010) inside a Python script (Appendix A). The first classification generated 259 galaxies which are seen as single galaxies in their K-band images. These galaxies were then reclassified based on image contouring in g, r, i, and K filters and therefore resulted in three categories of samples: Sample A (99 galaxies), Sample B (96 galaxies), and Sample C (64 galaxies).
Dark matter is an important part of cosmological matter, and gravitational lensing is a fundamental way to study the distribution of dark matter. Therefore, the gravitational lensing system is of ...great significance to the study of astrophysics. However, since strong gravitational lensing is extremely rare, the number of strong lensing candidate galaxies within the galaxy is also very large. To find these rare objects, we need to find them from at least tens of millions of images. The features based on the shallow structure are difficult to perfectly process these broad sense image data. In order to improve the efficiency and accuracy of recognition, a deep learning-based astronomical method for astronomical strong gravitational lensing systems is proposed, which first requests the classification of image data using label files. Next, data preprocessing is used for augmentation of targets in images, which provides more samples and more features can be learnt. After classification and preprocessing, the neural network is trained with the data, so as to facilitate the detection of strong lenses. By actual testing, the experiments show that the results of our method is 4.88% higher than Kapteyn Resnet and 7.5% higher than Manchester-SVM in model evaluation index AUC.
We present a multi-wavelength analysis of IRAS FSC10214+4724 from radio to X-ray wavelengths. This is a gravitationally lensed galaxy at a redshift z=2.3 (3 Gyr after the Big Bang) which hosts ...prodigious star formation as well as an obscured active nucleus. We derive a new lens model for the system employing a Bayesian Markov Chain Monte Carlo algorithm with extended-source, forward ray-tracing. An array of spatially resolved maps (radio, millimetre, near-infrared, optical) trace different physical components which enables a high resolution, multi-wavelength view of a high-redshift galaxy beyond the capabilities of current telescopes. The spatially-resolved molecular gas total intensity and velocity maps reveal a reasonably ordered system, however there is evidence for minor merger activity. We show evidence for an extended, low-excitation gas reservoir that either contains roughly half the total gas mass or has a different CO-to-H_2 conversion ratio. Very Long Baseline Interferometry (VLBI) is used to detect what we argue to be the obscured active nucleus with an effective angular resolution of <50 pc at z=2.3. The source plane inversion places the VLBI detection to within milli-arcseconds of the modeled cusp caustic, resulting in a very large magnification (mu > 70) which is over an order of magnitude larger than the derived co magnification. This implies an equivalent magnification difference between the starburst and AGN components, yielding significant distortion to the global continuum spectral energy distribution (SED). A primary result of this work is therefore the demonstration that emission regions of differing size and position within a galaxy can experience significantly different magnification factors (> 1 dex) and therefore distort our view of high-redshift, gravitationally lensed sources. This not only raises caution against unsophisticated uses of IRAS FSC10214+4724 as an archetype high-redshift Ultra-Luminous Infra-Red Galaxy (ULIRG), but also against statistical deductions based on samples of strong lenses with poorly constrained lens models and spatially-unresolved detections. Analogous to the continuum SED distortion quantified in this thesis, we predict a distortion of the CO spectral line energy distribution of IRAS FSC10214+4724 where higher order J lines, that are increasingly excited by the AGN and shock heating from the central starburst, will be preferentially lensed owing to their smaller solid angles and closer proximity to the AGN, and therefore the cusp of the caustic. This distortion is predicted to affect many high redshift lenses and will be tested most synergistically by the Jansky Very Large Array (JVLA) and the Atacama Large Millimetre Telescope (ALMA).
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