Gaia GraL: Gaia DR2 Gravitational Lens Systems. VI. Spectroscopic Confirmation and Modeling of Quadruply Imaged Lensed Quasars

Context. Thanks to its spatial resolution, the ESA/Gaia space mission offers a unique opportunity to discover new multiply imaged quasars and to study the already known lensed systems at sub-milliarcsecond astrometric precisions. Aims. In this paper, we address the detection of the known multiply imaged quasars from the Gaia Data Release 2 (DR2) and determine the astrometric and photometric properties of the individually detected images found in the Gaia DR2 catalogue. Methods. We have compiled an exhaustive list of quasar gravitational lenses from the literature to search for counterparts in the Gaia DR2. We then analysed the astrometric and photometric properties of these Gaia’s detections. To highlight the tremendous potential of Gaia at the sub-milliarcsecond level we finally performed a simple Bayesian modelling of the well-known gravitational lens system HE0435-1223, using Gaia DR2 and HST astrometry. Results. From 481 known multiply imaged quasars, 206 have at least one image found in the Gaia DR2. Among the 44 known quadruply imaged quasars of the list, 29 have at least one image in the Gaia DR2, 12 of which are fully detected (2MASX J01471020+4630433, HE 0435-1223, SDSS1004+4112, PG1115+080, RXJ1131-1231, 2MASS J11344050-2103230, 2MASS J13102005-1714579, B1422+231, J1606-2333, J1721+8842, WFI2033-4723, WGD2038-4008), eight have three counterparts, eight have two and one has only one. As expected, the modelling of HE0435-1223 shows that the model parameters are significantly better constrained when using Gaia astrometry compared to HST astrometry, in particular the relative positions of the background quasar source and the centroid of the deflector. The Gaia sub-milliarcsecond astrometry also significantly reduces the parameter correlations. Conclusions. Besides providing an up-to-date list of multiply imaged quasars and their detection in the Gaia DR2, this paper shows that more complex modelling scenarios will certainly benefit from Gaia sub-milliarcsecond astrometry.

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A centroid-based modelling approach to lens inversion for gravitationally lensed systems

USURJ University of Saskatchewan Undergraduate Research Journal ◽

10.32396/usurj.v6i2.402 ◽

2020 ◽

Vol 6 (2) ◽

Author(s):

Benjamen Smith ◽

Emery Dlugan

Keyword(s):

Image Processing ◽

Geometric Analysis ◽

Gravitational Lens ◽

Novel Method ◽

Processing Software ◽

Image Processing Software ◽

Gaia Dr2 ◽

Modelling Approach

In this research, we propose a novel method for determining the coordinate of a gravitational lens in systems where the lens has not yet been directly observed. Our technique uses image processing software to locate the optical centroid of strongly lensed systems and then applies a geometric analysis to derive the coordinates of the lens from the coordinates of the centroid and the arrangement of the lensed images. We demonstrate this method on gravitationally lensed quasar systems in which the lens has been observed to empirically validate our model, and then apply it to the GraL group's list of lensing candidates derived from Gaia DR2 to propose lens coordinates in these candidate systems.

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Gaia GraL: Gaia DR2 gravitational lens systems

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833337 ◽

2018 ◽

Vol 616 ◽

pp. L11 ◽

Cited By ~ 10

Author(s):

A. Krone-Martins ◽

L. Delchambre ◽

O. Wertz ◽

C. Ducourant ◽

F. Mignard ◽

...

Keyword(s):

Gravitational Lens ◽

Supervised Machine Learning ◽

Machine Learning Method ◽

Lens Model ◽

Learning Method ◽

Gravitational Lenses ◽

Extremely Randomized Trees ◽

Sky Survey ◽

Discovery Potential ◽

Gaia Dr2

Context. Multiply imaged gravitationally lensed quasars are among the most interesting and useful observable extragalactic phenomena. Because their study constitutes a unique tool in various fields of astronomy, they are highly sought, but difficult to find. Even in this era of all-sky surveys, discovering them remains a great challenge, with barely a few hundred systems currently known. Aims. We aim to discover new multiply imaged quasar candidates in the recently published Gaia Data Release 2 (DR2), which is the astrometric and photometric all-sky survey with the highest spatial resolution that achieves effective resolutions from 0.4″ to 2.2″. Methods. We cross-matched a merged list of quasars and candidates with Gaia DR2 and found 1 839 143 counterparts within 0.5″. We then searched matches with more than two Gaia DR2 counterparts within 6″. We further narrowed the resulting list using astrometry and photometry compatibility criteria between the Gaia DR2 counterparts. A supervised machine-learning method, called extremely randomized trees, was finally adopted to assign a probability of being lensed to each remaining system. Results. We report the discovery of two quadruply imaged quasar candidates that are fully detected in Gaia DR2. These are the most promising new quasar lens candidates from Gaia DR2 and a simple singular isothermal ellipsoid lens model is able to reproduce their image positions to within ~1 mas. This Letter demonstrates the discovery potential of Gaia for gravitational lenses.

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Gaia GraL: Gaia DR2 gravitational lens systems

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834573 ◽

2019 ◽

Vol 628 ◽

pp. A17 ◽

Cited By ~ 1

Author(s):

O. Wertz ◽

D. Stern ◽

A. Krone-Martins ◽

L. Delchambre ◽

C. Ducourant ◽

...

Keyword(s):

Time Delay ◽

Mass Density ◽

Position Angle ◽

Gravitational Lens ◽

Density Profiles ◽

Data Release ◽

The Impact ◽

Gaia Dr2 ◽

Different Levels

We report the spectroscopic confirmation and modeling of the quadruply imaged quasar GRAL 113100–441959, the first gravitational lens (GL) to be discovered from a machine learning technique that only relies on the relative positions and fluxes of the observed images without considering colour informations. Follow-up spectra obtained with Keck/LRIS reveal the lensing nature of this quadruply imaged quasar with redshift zs = 1.090 ± 0.002, but show no evidence of the central lens galaxy. Using the image positions and G-band flux ratios provided by Gaia Data Release 2 as constraints, we modeled the system with a singular power-law elliptical mass distribution (SPEMD) plus external shear, to different levels of complexity. We show that relaxing the isothermal constraint of the SPEMD does not lead to statistically significant different results in terms of fitting the lensing data. We thus simplified the SPEMD to a singular isothermal ellipsoid to estimate the Einstein radius of the main lens galaxy θE = 0.″851, the intensity and position angle of the external shear (γ,θγ) = (0.044, 11.°5), and we predict the lensing galaxy position to be (θgal,1, θgal,2) = (−0.″424, −0.″744) with respect to image A. We provide time delay predictions for pairs of images, assuming a plausible range of lens redshift values zl between 0.5 and 0.9. Finally, we examine the impact on time delays of the so-called source position transformation, a family of degeneracies existing between different mass density profiles that reproduce most of the lensing observables equally well. We show that this effect contributes significantly to the time delay error budget and cannot be ignored during the modeling. This has implications for robust cosmography applications of lensed systems. GRAL 113100–441959 is the first in a series of seven new spectroscopically confirmed GLs discovered from Gaia Data Release 2.

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Gaia GraL: Gaia DR2 Gravitational Lens Systems

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833802 ◽

2019 ◽

Vol 622 ◽

pp. A165 ◽

Cited By ~ 9

Author(s):

L. Delchambre ◽

A. Krone-Martins ◽

O. Wertz ◽

C. Ducourant ◽

L. Galluccio ◽

...

Keyword(s):

Supervised Learning ◽

Gravitational Lens ◽

Misclassification Rate ◽

Lens Model ◽

Learning Models ◽

Regular Grid ◽

Extremely Randomized Trees ◽

Data Release ◽

Additional Constraints ◽

Gaia Dr2

Aims. In this work, we aim to provide a reliable list of gravitational lens candidates based on a search performed over the entire Gaia Data Release 2 (Gaia DR2). We also aim to show that the astrometric and photometric information coming from the Gaia satellite yield sufficient insights for supervised learning methods to automatically identify strong gravitational lens candidates with an efficiency that is comparable to methods based on image processing. Methods. We simulated 106 623 188 lens systems composed of more than two images, based on a regular grid of parameters characterizing a non-singular isothermal ellipsoid lens model in the presence of an external shear. These simulations are used as an input for training and testing our supervised learning models consisting of extremely randomized trees (ERTs). These trees are finally used to assign to each of the 2 129 659 clusters of celestial objects extracted from the Gaia DR2 a discriminant value that reflects the ability of our simulations to match the observed relative positions and fluxes from each cluster. Once complemented with additional constraints, these discriminant values allow us to identify strong gravitational lens candidates out of the list of clusters. Results. We report the discovery of 15 new quadruply-imaged lens candidates with angular separations of less than 6″ and assess the performance of our approach by recovering 12 of the 13 known quadruply-imaged systems with all their components detected in Gaia DR2 with a misclassification rate of fortuitous clusters of stars as lens systems that is below 1%. Similarly, the identification capability of our method regarding quadruply-imaged systems where three images are detected in Gaia DR2 is assessed by recovering 10 of the 13 known quadruply-imaged systems having one of their constituting images discarded. The associated misclassification rate varies between 5.83% and 20%, depending on the image we decided to remove.

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Seti Space Missions

International Astronomical Union Colloquium ◽

10.1017/s0252921100015372 ◽

1997 ◽

Vol 161 ◽

pp. 761-776 ◽

Cited By ~ 1

Author(s):

Claudio Maccone

Keyword(s):

Electromagnetic Waves ◽

Space Missions ◽

Gravitational Lens ◽

The Sun ◽

Space Antenna ◽

Focal Distance ◽

Large Space ◽

The Earth ◽

Space Antennas ◽

New Space

AbstractSETI from space is currently envisaged in three ways: i) by large space antennas orbiting the Earth that could be used for both VLBI and SETI (VSOP and RadioAstron missions), ii) by a radiotelescope inside the Saha far side Moon crater and an Earth-link antenna on the Mare Smythii near side plain. Such SETIMOON mission would require no astronaut work since a Tether, deployed in Moon orbit until the two antennas landed softly, would also be the cable connecting them. Alternatively, a data relay satellite orbiting the Earth-Moon Lagrangian pointL2would avoid the Earthlink antenna, iii) by a large space antenna put at the foci of the Sun gravitational lens: 1) for electromagnetic waves, the minimal focal distance is 550 Astronomical Units (AU) or 14 times beyond Pluto. One could use the huge radio magnifications of sources aligned to the Sun and spacecraft; 2) for gravitational waves and neutrinos, the focus lies between 22.45 and 29.59 AU (Uranus and Neptune orbits), with a flight time of less than 30 years. Two new space missions, of SETI interest if ET’s use neutrinos for communications, are proposed.

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