[Paper Review] Gaia GraL II - Gaia DR2 Gravitational Lens Systems: The Known Multiply Imaged Quasars

C. Ducourant, O. Wertz+13 more|Open Repository and Bibliography (University of Liège)|May 18, 2018

Gamma-ray bursts and supernovae23 references11 citations

TL;DR

This paper identifies and analyzes 200 known multiply imaged quasars from the Gaia DR2 catalog, detecting at least one image in 200 of 478 known systems, with 12 quadruply-imaged quasars fully detected. Using Gaia's sub-milliarcsecond astrometry, the study demonstrates significantly improved constraints on lens model parameters—especially relative source and deflector positions—and reduced parameter correlations compared to HST data, highlighting Gaia's transformative potential for strong gravitational lensing studies.

ABSTRACT

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. In this paper, we address the detection of the known multiply-imaged quasars from the Gaia Data Release 2 and determine the astrometric and photometric properties of the individually detected images found in the Gaia DR2 catalogue. We have compiled an exhaustive list of quasar gravitational lenses from the literature to search for counterparts in the Gaia Data Release 2. We then analyze the astrometric and photometric properties of these Gaia's detections. To highlight the tremendous potential of Gaia at the sub-milliarcsecond level we finally perform a simple Bayesian modeling of the well-known gravitational lens system HE0435-1223, using Gaia Data Release 2 and HST astrometry. From 478 known multiply imaged quasars, 200 have at least one image found in the Gaia Data Release 2. Among the 41 known quadruply-imaged quasars of the list, 26 have at least one image in the Gaia Data Release 2, 12 of which are fully detected, 6 have three counterparts, 7 have two and 1 has only one. As expected, the modeling 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. Besides providing an up-to-date list of multiply imaged quasars and their detection in the Gaia DR2, this paper shows that more complex modeling scenarios will certainly benefit from Gaia sub-milliarcsecond astrometry.

Motivation & Objective

• To compile a comprehensive list of known multiply imaged quasars and assess their detectability in Gaia DR2.
• To determine the astrometric and photometric properties of individually detected images from Gaia DR2 for known lensed quasars.
• To evaluate the impact of Gaia's sub-milliarcsecond astrometry on improving constraints in strong gravitational lens modeling compared to Hubble Space Telescope (HST) data.
• To demonstrate the potential of future Gaia Data Releases for advancing the study of strong gravitational lensing.
• To provide a publicly accessible, up-to-date catalog of known lensed quasars with Gaia DR2 detection status and astrometric/photometric data.

Proposed method

• Compiled an exhaustive list of 478 known or candidate multiply imaged quasars from the literature.
• Cross-matched this list with the Gaia DR2 astrometric catalogue to identify counterparts.
• Analyzed the astrometric and photometric properties of all detected images in Gaia DR2.
• Performed a Bayesian modeling of the well-known lens system HE0435-1223 using both Gaia DR2 and HST astrometry.
• Compared model parameter constraints and correlations between Gaia DR2 and HST data to quantify improvements.
• Utilized the NSIEg lens model to assess the precision of source position and deflector centroid estimation.

Experimental results

Research questions

• RQ1 How many known multiply imaged quasars from the literature are detected in Gaia DR2?
• RQ2 What is the astrometric and photometric quality of the detected images in Gaia DR2 for known lensed quasars?
• RQ3 To what extent does Gaia DR2 sub-milliarcsecond astrometry improve the constraints on lens model parameters compared to HST astrometry?
• RQ4 How do parameter correlations in lens models change when using Gaia DR2 data instead of HST data?
• RQ5 What fraction of known quadruply-imaged quasars are fully detected in Gaia DR2, and what is the expected improvement in future Gaia Data Releases?

Key findings

• Out of 478 known or candidate multiply imaged quasars, 200 have at least one image detected in Gaia DR2.
• Among the 41 known quadruply-imaged quasars, 26 have at least one image in Gaia DR2, with 12 fully detected (all four images present).
• The Bayesian modeling of HE0435-1223 shows that Gaia DR2 astrometry significantly improves the constraint on the relative position between the quasar source and the deflector centroid.
• Gaia DR2 astrometry reduces parameter correlations in the lens model compared to HST astrometry, leading to more robust and precise solutions.
• The study demonstrates that Gaia DR2 provides almost an order of magnitude improvement in astrometric precision over typical HST observations for lensed quasars.
• The results indicate that future Gaia Data Releases (DR3 and DR4) will further enhance the detection and characterization of lensed quasars due to improved spatial resolution and data quality.