Spectroscopic confirmation and modelling of two lensed quadruple quasars in the Dark Energy Survey public footprint

Spiniello, C.; Sergeyev, A. V.; Marchetti, L.; Tortora, C.; Napolitano, N. R.; Shalyapin, V.; Agnello, A.; Getman, F. I.; Vaccari, M.; Serjeant, S.; Koopmans, L. V. E.; Baker, A. J.; Jarrett, T. H.; Covone, G. and Vernardos, G. (2019). Spectroscopic confirmation and modelling of two lensed quadruple quasars in the Dark Energy Survey public footprint. Monthly Notices of the Royal Astronomical Society, 485(4) pp. 5086–5095.

DOI: https://doi.org/10.1093/mnras/stz781


Quadruply lensed quasars are extremely rare objects, but incredibly powerful cosmological tools. Only few dozen are known in the whole sky. Here we present the spectroscopic confirmation of two new quadruplets WG0214-2105 and WG2100-4452 discovered by Agnello & Spiniello (2018) within the Dark Energy Survey public footprints. We have conducted spectroscopic follow-up of these systems with the Southern African Large Telescope as part of a program that aims at confirming the largest possible number of strong gravitational lenses in the equatorial and southern hemisphere. For both systems, we present the sources spectra that allowed us to estimate their redshifts and unambiguously confirm their lensing nature. For the brighter deflector (WG2100-4452) we measure the spectroscopic redshift and the stellar velocity dispersion from optical absorption lines in the spectrum. For the other system we infer the lens redshift from photometry, being the quality of the spectra not good enough. We obtain photometry for both lenses, directly from multi-band images, isolating the lenses from the quasars. One of the quadruplets, WG0214-2105, was also observed by Pan-STARRS, allowing us to estimate the apparent brightness of each quasar image at two different epochs, and thus to find evidence for flux variability. This result could suggest a microlensing event for the faintest components, although intrinsic variability cannot be excluded with only two epochs. Finally, we present simple lens models for both quadruplets, obtaining Einstein radii, SIE velocity dispersions, ellipticities, and position angles of the lenses, as well as time delay predictions assuming a concordance cosmological model.

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