Gravitationally lensed quasars in Gaia - II. Discoveryof 24 lensed quasars


Type
Article
Change log
Authors
Lemon, CA 
Auger, MW 
McMahon, RG 
Ostrovski, F 
Abstract

We report the discovery, spectroscopic confirmation and preliminary characterisation of 24 gravitationally lensed quasars identified using Gaia observations. Candidates were selected in the Pan-STARRS footprint with quasar-like WISE colours or as photometric quasars from SDSS, requiring either multiple detections in Gaia or a single Gaia detection near a morphological galaxy. The Pan-STARRS grizY images were modelled for the most promising candidates and 60 candidate systems were followed up with the William Herschel Telescope. 13 of the lenses were discovered as Gaia multiples and 10 as single Gaia detections near galaxies. We also discover 1 lens identified through a quasar emission line in an SDSS galaxy spectrum. The lenses have median image separation 2.13 arcsec and the source redshifts range from 1.06 to 3.36. 4 systems are quadruply-imaged and 20 are doubly-imaged. Deep CFHT data reveal an Einstein ring in one double system. We also report 12 quasar pairs, 10 of which have components at the same redshift and require further follow-up to rule out the lensing hypothesis. We compare the properties of these lenses and other known lenses recovered by our search method to a complete sample of simulated lenses to show the lenses we are missing are mainly those with small separations and higher source redshifts. The initial Gaia data release only catalogues all images of ~ 30% of known bright lensed quasars, however the improved completeness of Gaia data release 2 will help find all bright lensed quasars on the sky.

Description
Keywords
gravitational lensing: strong, methods: observational, quasars: general
Journal Title
Monthly Notices of the Royal Astronomical Society
Conference Name
Journal ISSN
0035-8711
1365-2966
Volume Title
479
Publisher
Oxford University Press (OUP)
Rights
Publisher's own licence
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (1638336)
Science and Technology Facilities Council (ST/K004182/1)
Science and Technology Facilities Council (ST/N001702/1)