Discovery of two gravitationally lensed quasars in the Dark Energy Survey

A. Agnello , T. Treu , F. Ostrovski , P. L. Schechter , E. J. Buckley-Geer , H. Lin , M. W. Auger , F. Courbin , C. D. Fassnacht , J. Frieman , N. Kuropatkin , P. J. Marshall , R. G. Mcmahon , G. Meylan , A. More , S. H. Suyu , C. E. Rusu , D. Finley , T. Abbott , F. B. Abdalla , S. Allam , J. Annis , M. Banerji , A. Benoit-Lévy , E. Bertin (1) , D. Brooks , D. L. Burke , A. Carnero Rosell , M. Carrasco Kind , J. Carretero , C. E. Cunha , C. B. d'Andrea , L. N. da Costa , S. Desai , H. T. Diehl , J. P. Dietrich , P. Doel , T. F. Eifler , J. Estrada , A. Fausti Neto , B. Flaugher , P. Fosalba , D. W. Gerdes , D. Gruen , G. Gutierrez , K. Honscheid , D. J. James , K. Kuehn , O. Lahav , M. Lima , M. A. G. Maia , M. March , J. L. Marshall , P. Martini , P. Melchior , C. J. Miller , R. Miquel , R. C. Nichol , R. Ogando , A. A. Plazas , K. Reil , A. K. Romer , A. Roodman , M. Sako , E. Sanchez , B. Santiago , V. Scarpine , M. Schubnell , I. Sevilla-Noarbe , R. C. Smith , M. Soares-Santos , F. Sobreira , E. Suchyta , M. E. C. Swanson , G. Tarle , J. Thaler , D. Tucker , A. R. Walker , R. H. Wechsler , Y. Zhang

1 IAP - Institut d'Astrophysique de Paris

We present spectroscopic confirmation of two new gravitationally lensed quasars, discovered in the Dark Energy Survey (DES) and Wide-field Infrared Survey Explorer (WISE) based on their multiband photometry and extended morphology in DES images. Images of DES J0115-5244 show a red galaxy with two blue point sources at either side, which are images of the same quasar at z_s = 1.64 as obtained by our long-slit spectroscopic data. The Einstein radius estimated from the DES images is 0.51 arcsec. DES J2146-0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fibre spectrum shows a quasar component at z_s = 2.38 and absorption by Mg II and Fe II at z_l = 0.799, which we tentatively associate with the foreground lens galaxy. Our long-slit spectra show that the blue components are resolved images of the same quasar. The Einstein radius is 0.68 arcsec, corresponding to an enclosed mass of 1.6 × 10¹¹ M_⊙. Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data mining and model-based selection that is being applied to the entire DES data set.

Keywords: gravitational lensing: strong; methods: observational; methods: statistical; quasars: emission lines; Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

A. Agnello, T. Treu, F. Ostrovski, P. L. Schechter, E. J. Buckley-Geer, et al.. Discovery of two gravitationally lensed quasars in the Dark Energy Survey. Monthly Notices of the Royal Astronomical Society, 2015, 454, pp.1260-1265. ⟨10.1093/mnras/stv2171⟩. ⟨insu-03644675⟩