scholarly journals Auto-identification of unphysical source reconstructions in strong gravitational lens modelling

2021 ◽  
Author(s):  
Jacob Maresca ◽  
Simon Dye ◽  
Nan Li
Keyword(s):  
High Redshift ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Machine Learning Techniques ◽  
Source Surface ◽  
Parametric Modelling ◽  
Irregular Structure ◽  
Reconstruction Methods ◽  
Auto Identification ◽  
Automated Procedures

Abstract With the advent of next-generation surveys and the expectation of discovering huge numbers of strong gravitational lens systems, much effort is being invested into developing automated procedures for handling the data. The several orders of magnitude increase in the number of strong galaxy-galaxy lens systems is an insurmountable challenge for traditional modelling techniques. Whilst machine learning techniques have dramatically improved the efficiency of lens modelling, parametric modelling of the lens mass profile remains an important tool for dealing with complex lensing systems. In particular, source reconstruction methods are necessary to cope with the irregular structure of high-redshift sources. In this paper, we consider a Convolutional Neural Network (CNN) that analyses the outputs of semi-analytic methods which parametrically model the lens mass and linearly reconstruct the source surface brightness distribution. We show the unphysical source reconstructions that arise as a result of incorrectly initialised lens models can be effectively caught by our CNN. Furthermore, the CNN predictions can be used to automatically re-initialise the parametric lens model, avoiding unphysical source reconstructions. The CNN, trained on reconstructions of lensed Sérsic sources, accurately classifies source reconstructions of the same type with a precision P > 0.99 and recall R > 0.99. The same CNN, without re-training, achieves P = 0.89 and R = 0.89 when classifying source reconstructions of more complex lensed HUDF sources. Using the CNN predictions to re-initialise the lens modelling procedure, we achieve a 69 per cent decrease in the occurrence of unphysical source reconstructions. This combined CNN and parametric modelling approach can greatly improve the automation of lens modelling.

scholarly journals When Darwin Met Einstein: Gravitational Lens Inversion with Genetic Algorithms

2005 ◽  
Vol 22 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Brendon J. Brewer ◽  
Geraint F. Lewis
Keyword(s):  
Genetic Algorithms ◽  
Gravitational Lensing ◽  
Surface Brightness ◽  
Initial Study ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Atmospheric Effects ◽  
Lens Model ◽  
New Approach ◽  
Genetic Algorithm Approach

AbstractGravitational lensing can magnify a distant source, revealing structural detail which is normally unresolvable. Recovering this detail through an inversion of the influence of gravitational lensing, however, requires optimisation of not only lens parameters, but also of the surface brightness distribution of the source. This paper outlines a new approach to this inversion, utilising genetic algorithms to reconstruct the source profile. In this initial study, the effects of image degradation due to instrumental and atmospheric effects are neglected and it is assumed that the lens model is accurately known, but the genetic algorithm approach can be incorporated into more general optimisation techniques, allowing the optimisation of both the parameters for a lensing model and the surface brightness of the source.

scholarly journals ADAPTIVE OPTICS OBSERVATIONS OF B0128+437: A LOW-MASS, HIGH-REDSHIFT GRAVITATIONAL LENS

2010 ◽  
Vol 716 (2) ◽  
pp. L185-L189 ◽  
Author(s):  
David J. Lagattuta ◽  
Matthew W. Auger ◽  
Christopher D. Fassnacht
Keyword(s):  
Adaptive Optics ◽  
High Redshift ◽  
Gravitational Lens ◽  
Low Mass

scholarly journals Gravitational microlensing of an elliptical source near a fold caustic

2018 ◽  
pp. 10-15
Author(s):  
A. Alexandrov ◽  
V. Zhdanov ◽  
A. Kuybarov
Keyword(s):  
Amplification Factor ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Variable Component ◽  
Extended Source ◽  
Elliptical Shape ◽  
Gravitational Microlensing ◽  
Gaussian Source ◽  
Analogous Formula ◽  
Circular Source

We consider the amplification factor for the luminosity of an extended source near the fold caustic of the gravitational lens. It is assumed that the source has elliptical shape, and the brightness distribution along the radial directions is Gaussian. During the microlensing event the total brightness of all microimages is observed, which changes when the source moves relative to the caustic. The main contribution to the variable component is given by the so-called critical images that arise/disappear at the intersection of the caustic by the source. In the present paper we obtained an analogous formula for elliptical Gaussian source. The formula involves a dependence on the coordinates of the source centre, its geometric dimensions, and its orientation relative to the caustic. We show that in the linear caustic approximation the amplification of the circular and elliptical sources is described by the same (rescaled) formula. However, in the next approximations the differences are significant. We compare analytical calculations of the amplification curves for different orientations of an elliptical source and for a circular source with the same luminosity for the model example.

scholarly journals Systematic errors in strong gravitational lensing reconstructions, a numerical simulation perspective

2020 ◽  
Vol 496 (2) ◽  
pp. 1718-1729 ◽  
Author(s):  
Wolfgang Enzi ◽  
Simona Vegetti ◽  
Giulia Despali ◽  
Jen-Wei Hsueh ◽  
R Benton Metcalf
Keyword(s):  
Gravitational Lensing ◽  
Time Delays ◽  
Surface Brightness ◽  
Mass Density ◽  
Control Sample ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Galactic Potentials ◽  
Fractional Error ◽  
Approximate Bayesian

ABSTRACT We present the analysis of a sample of 24 SLACS-like galaxy–galaxy strong gravitational lens systems with a background source and deflectors from the Illustris-1 simulation. We study the degeneracy between the complex mass distribution of the lenses, substructures, the surface brightness distribution of the sources, and the time delays. Using a novel inference framework based on Approximate Bayesian Computation, we find that for all the considered lens systems, an elliptical and cored power-law mass density distribution provides a good fit to the data. However, the presence of cores in the simulated lenses affects most reconstructions in the form of a Source Position Transformation. The latter leads to a systematic underestimation of the source sizes by 50 per cent on average, and a fractional error in H0 of around $25_{-19}^{+37}$ per cent. The analysis of a control sample of 24 lens systems, for which we have perfect knowledge about the shape of the lensing potential, leads to a fractional error on H0 of $12_{-3}^{+6}$ per cent. We find no degeneracy between complexity in the lensing potential and the inferred amount of substructures. We recover an average total projected mass fraction in substructures of fsub < 1.7–2.0 × 10−3 at the 68 per cent confidence level in agreement with zero and the fact that all substructures had been removed from the simulation. Our work highlights the need for higher resolution simulations to quantify the lensing effect of more realistic galactic potentials better, and that additional observational constraint may be required to break existing degeneracies.

scholarly journals The 2dF Gravitational Lens Survey

2001 ◽  
Vol 18 (2) ◽  
pp. 192-194 ◽  
Author(s):  
Daniel J. Mortlock ◽  
Darren S. Madgwick ◽  
Ofer Lahav
Keyword(s):  
Cross Correlation ◽  
High Redshift ◽  
Point Sources ◽  
Gravitational Lens ◽  
Multiple Point ◽  
Quasar Spectra ◽  
Redshift Survey ◽  
Galaxy Redshift ◽  
Components Analysis ◽  
Correlation Techniques

AbstractThe 2 degree Field (2dF) galaxy redshift survey will involve obtaining spectra of approximately 2.5 105 objects which have previously been identified as galaxy candidates on morphological grounds. Included in these spectra should be about ten gravitationally-lensed quasars, all with low-redshift galaxies as deflectors (as the more common lenses with high-redshift deflectors will be rejected from the survey as multiple point-sources). The lenses will appear as superpositions of galaxy and quasar spectra, and either cross-correlation techniques or principal components analysis should be able to identify candidates systematically. With the 2dF survey approximately half-completed it is now viable to begin a methodical search for these spectroscopic lenses, and the first steps of this project are described here.

scholarly journals The host galaxy of the short GRB 111117A at z = 2.211

2018 ◽  
Vol 616 ◽  
pp. A48 ◽  
Author(s):  
J. Selsing ◽  
T. Krühler ◽  
D. Malesani ◽  
P. D’Avanzo ◽  
S. Schulze ◽  
...  
Keyword(s):  
High Redshift ◽  
Brightness Distribution ◽  
Host Galaxy ◽  
Physical Parameters ◽  
Imaging Data ◽  
Redshift Distribution ◽  
Time Model ◽  
Age Of The Universe ◽  
Element Enrichment ◽  
The Universe

It is notoriously difficult to localize short γ-ray bursts (sGRBs) and their hosts to measure their redshifts. These measurements, however, are critical for constraining the nature of sGRB progenitors, their redshift distribution, and the r-process element enrichment history of the universe. Here we present spectroscopy of the host galaxy of GRB 111117A and measure its redshift to be z = 2.211. This makes GRB 111117A the most distant high-confidence short duration GRB detected to date. Our spectroscopic redshift supersedes a lower, previously estimated photometric redshift value for this burst. We use the spectroscopic redshift, as well as new imaging data to constrain the nature of the host galaxy and the physical parameters of the GRB. The rest-frame X-ray derived hydrogen column density, for example, is the highest compared to a complete sample of sGRBs and seems to follow the evolution with redshift as traced by the hosts of long GRBs. From the detection of Lyα emission in the spectrum, we are able to constrain the escape fraction of Lyα in the host. The host lies in the brighter end of the expected sGRB host brightness distribution at z = 2.211, and is actively forming stars. Using the observed sGRB host luminosity distribution, we find that between 43% and 71% of all Swift-detected sGRBs have hosts that are too faint at z ~ 2 to allow for a secure redshift determination. This implies that the measured sGRB redshift distribution could be incomplete at high redshift. The high z of GRB 111117A is evidence against a lognormal delay-time model for sGRBs through the predicted redshift distribution of sGRBs, which is very sensitive to high-z sGRBs. From the age of the universe at the time of GRB explosion, an initial neutron star (NS) separation of a0 < 3.1 R⊙ is required in the case where the progenitor system is a circular pair of inspiralling NSs. This constraint excludes some of the longest sGRB formation channels for this burst.

scholarly journals Effect of the sourse ellipticity on light curves in extragalactic gravitational lens systems

2020 ◽  
pp. 6-10
Author(s):  
V. Zhdanov ◽  
A. Alexandrov
Keyword(s):  
Brightness Distribution ◽  
Light Curves ◽  
Gravitational Lens ◽  
Lens System ◽  
Real Form ◽  
Gravitational Microlensing ◽  
Bulk Motion ◽  
Centrally Symmetric ◽  
Relative Delay ◽  
Characteristic Values

In extragalactic gravitational lens system (GLS) several macro-images of a remote source (quasar) are observed. Gravitational microlensing leads to uncorrelated brightness variations of the macro-images. These variations can be separated from proper brightness changes of the source, which are repeated in each image with some relative delay. In most papers the gravitational microlensing effects in extragalactic GLS typically deal with centrally symmetric sources, though the real form of the source can be more complicated. In this paper we consider statistical signals of the source ellipticity in light curves of microlensed objects, which arise as a result of observations of many high amplification events. As a first step, we consider a qualitative version of the problem, when an elliptic source with Gaussian brightness distribution is crossed by a number of simple (fold) caustics with different orientations. Also we assume that the caustic network is isotropic, that is all orientations of the caustics and directions of their velocities are equally possible. We use the linear fold caustic approximation for the amplification of a small point source, when two critical images appear/disappear after the caustic crossing. For a rough estimate, the strength and velocity of the caustic are fixed by certain characteristic values. We estimate the averaged light curve after many caustic crossing events and compare maxima of brightness on the light curves for different eccentricities of the source. The ellipticity signal in the light curves is noticeable for a considerable oblateness of the source. Though we expect that the effect will be smeared out after taking into account the distribution of the caustic velocities and caustic strengths. Possible complications of the problem are indicated due to interplay of effects due to velocity distribution of stars in the lensing galaxy and bulk motion of the lensing galaxy as a whole.

scholarly journals The Hamburg/ESO Survey for Bright QSOs — Slitless Spectroscopy at High Resolution

1994 ◽  
Vol 161 ◽  
pp. 723-727 ◽  
Author(s):  
L. Wisotzki
Keyword(s):  
High Resolution ◽  
High Redshift ◽  
Gravitational Lens ◽  
High Resolution Spectroscopy ◽  
Wide Angle ◽  
X Rays ◽  
Digital Revolution ◽  
First Results ◽  
Objective Prism

The digital revolution in the evaluation of photographic plates and the introduction of automated quasar search techniques have drastically increased the number of known QSOs over the past decade. However, most of these QSOs are so faint that their use is limited to statistical studies. The bright end of the quasar population is still dominated by objects selected in other wavebands, such as radio, X-rays, or even infrared. We have started in 1990 a wide-angle objective-prism survey (the Hamburg/ESO Survey, HES) using the 1 m ESO Schmidt telescope (Reimers 1990). The survey is intended to cover 5000 deg2, of which about a third has been acquired up to now. The prime goal is to compile a large sample of bright (B &lt; 17.5) QSOs suited for detailed follow-up studies, in particular for high-resolution spectroscopy. Other objectives are to search for gravitational lens candidates and to directly measure the local luminosity function of quasars. In each Schmidt field, a spectral and a direct plate are scanned with the PDS 1010G microdensitometer at Hamburg, followed by an automated candidate selection and subsequent follow-up spectroscopy with the ESO 1.52 m and 3.6 m telescopes. A novel feature in our survey is the use of an objective-prism with a dispersion of 450 å/mm at Hγ, yielding a seeing-limited spectral resolution of 10–20 å FWHM. A full documentation of the survey techniques is in preparation. First results include the discoveries of the second-brightest QSO in the south (Wisotzki et al. 1991), and of a bright double QSO at high redshift, probably a gravitational lens (Wisotzki et al. 1993). In this contribution I want to show how a wide-angle quasar survey like the HES can benefit from the high resolution of the survey spectra.

scholarly journals HCN Observations of Submillimeter Galaxies and QSOs at High Redshift

2006 ◽  
Vol 2 (S235) ◽  
pp. 403-403
Author(s):  
Yu Gao ◽  
C.L. Carilli ◽  
P.M. Solomon ◽  
P.A. Vanden Bout
Keyword(s):  
High Redshift ◽  
Gravitational Lens ◽  
Continuum Emission ◽  
Upper Limits ◽  
Submillimeter Galaxies

We have conducted sensitive HCN(1-0) line observations of four high redshift submillimeter (sub-mm) galaxies and QSOs with the VLA. Although none is significantly detected in either line or continuum emission, thanks to the gravitational lens, sub-mm galaxy SMM J16359+6612 is marginally (at the 3-4σ level) detected once the three lensed components are stacked up. The HCN source appears to be double with a separation of ~1.5'', consistent with what has been implied from other observations. This first possible HCN detection of a submm galaxy, and three stringent HCN upper limits, combined with previous HCN detections and upper limits strongly constrain the HCN/CO ratios at high-z to be comparable to that of local ULIRGs.

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