Gaia GraL: Gaia DR2 gravitational lens systems

Abstract

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 z s = 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 θ E = 0. 851, the intensity and position angle of the external shear (γ, θ γ ) = (0.044, 11. • 5), and we predict the lensing galaxy position to be (θ gal,1 , θ gal,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 z l 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.

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

“…GraL J113100.0−442000 -This system was modeled in GraL IV (Wertz et al 2019). The models presented here agree with the previous ones.…”

“…GraL J113100.0−442000 -This is the quadruply-imaged quasar presented as a candidate in Krone-Martins et al ( 2018) and Delchambre et al (2019), and then spectroscopically confirmed and modelled in Wertz et al (2019). The latter is a detailed paper dedicated to this single source.…”

“…The source is at intermediate redshift, z = 1.090, and the Keck spectroscopy shows no evidence of the central lens galaxy. Gemini IFU observations separated the two quasar images with the smallest angular separation, called A and B in Wertz et al (2019), as seen in Fig. 3.…”

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

“…The system 11310013-1149559935 has been observed to have a timing variation indicative of gravitational lensing [10]. Our data then agrees well with this additional evidence, as we have demonstrated this system has geometric properties consistent with lensing.…”

Gaia: The Galaxy in six (and more) dimensions

“…According to the NASA ADS, the majority of the new publications are related to the fields of Galactic halo and disk studies (see below), but also to solar system studies (Cellino et al, 2007;Gaia Collaboration et al, 2018d), exoplanet and host star characterization (Kervella et al, 2019), characterization of variable or binary objects (Ziegler et al, 2018) and of objects with astroseismological data (Berger et al, 2018). Work was done also in the field of extragalactic studies, for example on Quasars variability (Hwang et al, 2019) or gravitational lensing (Wertz et al, 2019). Gaia DR2 data have even been used to search for a plausible home star for the interstellar object 'Oumuamua (Bailer-Jones et al, 2018), which recently was discovered transiting in the solar system 12 .…”