Serendipitous discovery of quadruply-imaged quasars: two diamonds

TL;DR

This paper reports the serendipitous discovery of two quadruply-imaged quasars through visual inspection of galaxy images, with follow-up spectroscopy confirming one as a lensed quasar at z=1.975, demonstrating a novel lens detection method.

Contribution

The study introduces a new lens discovery approach by inspecting galaxy images for lensing features, complementing traditional color-based methods.

Findings

Confirmed one quadruply-imaged quasar at z=1.975

Identified a highly sheared quadruply-imaged quasar candidate

Discovered about a dozen potential lensing galaxies serendipitously

Abstract

Gravitationally lensed quasars are powerful and versatile astrophysical tools, but they are challengingly rare. In particular, only ~25 well-characterized quadruple systems are known to date. To refine the target catalogue for the forthcoming Taipan Galaxy Survey, the images of a large number of sources are being visually inspected in order to identify objects that are confused by a foreground star or galaxies that have a distinct multi-component structure. An unexpected by-product of this work has been the serendipitous discovery of about a dozen galaxies that appear to be lensing quasars, i.e. pairs or quartets of foreground stellar objects in close proximity to the target source. Here we report two diamond-shaped systems. Follow-up spectroscopy with the IMACS instrument on the 6.5m Magellan Baade telescope confirms one of these as a z = 1.975 quasar quadruply lensed by a double galaxy at z = 0.293. Photometry from publicly available survey images supports the conclusion that the other system is a highly sheared quadruply-imaged quasar. In starting with objects thought to be galaxies, our lens finding technique complements the conventional approach of first identifying sources with quasar-like colours and subsequently finding evidence of lensing.