DES meets Gaia: discovery of strongly lensed quasars from a multiplet search

Abstract

We report the discovery, spectroscopic confirmation and first lens models of the first two, strongly lensed quasars from a combined search in WISE and Gaia over the DES footprint. The four-image lensWGD2038-4008 (r.a.=20:38:02.65, dec.=-40:08:14.64) has source- and lens-redshifts $z_s=0.777\pm 0.001$ and $z_l=0.230\pm 0.002$ respectively. Its deflector has effective radius $R_{\mathrm{eff}}\approx 3.4^{\prime \prime }$, stellar mass $\log (M_{\star }/M_{\odot })=11.64_{-0.43}^{+0.20}$, and shows extended isophotal shape variation. Simple lens models yield Einstein radii $R_{\mathrm{E}}=(1.30\pm 0.04{)}^{\prime \prime },$ axis ratio $q=0.75\pm 0.1$ (compatible with that of the starlight) and considerable shear-ellipticity degeneracies. The two-image lensWGD2021-4115 (r.a.=20:21:39.45, dec.=--41:15:57.11) has $z_s=1.390\pm 0.001$ and $z_l=0.335\pm 0.002$, and Einstein radius $R_{\mathrm{E}}=(1.1\pm 0.1{)}^{\prime \prime },$ but higher-resolution imaging is needed to accurately separate the deflector and faint quasar image. We also show high-rank candidate doubles selected this way, some of which have been independently identified with different techniques, and discuss a DES+WISE quasar multiplet selection.

MNRAS subm. 21/10/2017, awaiting reviewer selection. This paper has been approved by DES Collaboration-Wide Review