Spectroscopic follow-up of the quadruply lensed quasar WGD2038-4008/GRAL2038-4008
Abstract
We present independent optical spectroscopic follow-up of WGD2038-4008/GRAL2038-4008, a background quasar strongly lensed by a foreground elliptical galaxy into four images, recently discovered independently by Agnello et al. [2018, MNRAS, 479, 4345] and Krone-Martins et al. [2018, A&A, 616, L11] thanks to the exquisite spatial resolution of Gaia. The quasar images are bright (i ∼ 19 mag), thus enabling us to reach S/N > 20 for the continuum within 30 min of exposure time with the Andalucia Faint Object Spectrograph and Camera spectrograph mounted on the 2.56-m Nordic Optical Telescope. The flexible scheduling and high sensitivity delivered by Andalucia Faint Object Spectrograph and Camera provide timely redshifts and reveal the nature of the quasar images; both are essential for lensing modelling and cosmography. Our analysis shows a strong emission feature in a data gap in Agnello et al. [2018, MNRAS, 479, 4345], which can be attributed to as an interloper emission line feature from the foreground lensing galaxy, or hinting to a higher redshift of the background quasar. We discuss these two scenarios and outline possible tests to verify these scenarios.
- Publication:
-
Publications of the Astronomical Society of Australia
- Pub Date:
- March 2019
- DOI:
- 10.1017/pasa.2019.4
- Bibcode:
- 2019PASA...36...11L
- Keywords:
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- catalogues;
- gravitational lensing: strong;
- quasars: general;
- surveys;
- techniques: image processing