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Post Info TOPIC: DES J0408-5354


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Title: Models of the strongly lensed quasar DES J0408-5354
Author: Adriano Agnello, Huan Lin, L. Buckley-Geer, T. Treu, V. Bonvin, F. Courbin, C. Lemon, T. Mori****a, A. Amara, M.W. Auger, S. Birrer, J. Chan, T. Collett, A. More, C.D. Fassnacht, J. Frieman, P.J. Marshall, R.G. McMahon, G. Meylan, S.H. Suyu, F.Castander, D. Finley, A.Howell, C. Kochanek, M. Makler, P. Martini, N. Morgan, B.Nord, F. Ostrovski, P. Schechter, D. Tucker, R. Wechsler, T. M. C. Abbott, F. B. Abdalla, S. Allam, A. Benoit-Lévy, E. Bertin, D. Brooks, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, M. Crocce, C. E. Cunha, C. B. D'Andrea, L. N. da Costa, S. Desa, J. P. Dietrich, T. F. Eifler, B. Flaugher, P. Fosalba, J. García-Bellido, E. Gaztanaga, D. A. Goldstein, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, K. Honscheid, D. J. James, K. Kuehn, et al. (24 additional authors not shown)

We present gravitational lens models of the multiply imaged quasar DES J0408-5354, recently discovered in the Dark Energy Survey (DES) footprint, with the aim of interpreting its remarkable quad-like configuration. We first model the DES single-epoch grizY images as a superposition of a lens galaxy and four point-like objects, obtaining spectral energy distributions (SEDs) and relative positions for the objects. Three of the point sources (A,B,D) have SEDs compatible with the discovery quasar spectra, while the faintest point-like image (G2/C) shows significant reddening and a 'grey' dimming of \approx 0.8mag. In order to understand the lens configuration, we fit different models to the relative positions of A,B,D. Models with just a single deflector predict a fourth image at the location of G2/C but considerably brighter and bluer. The addition of a small satellite galaxy (RE \approx 0.2") in the lens plane near the position of G2/C suppresses the flux of the fourth image and can explain both the reddening and grey dimming. All models predict a main deflector with Einstein radius between 1.7" and 2.0", velocity dispersion 267-280km/s and enclosed mass \approx 6 x 10^11 solar masses, even though higher resolution imaging data are needed to break residual degeneracies in model parameters. The longest time-delay (B-A) is estimated as \approx 85 (resp. \approx 25) days by models with (resp. without) a perturber near G2/C. The configuration and predicted time-delays of J0408-5354 make it an excellent target for follow-up aimed at understanding the source quasar host galaxy and substructure in the lens, and measuring cosmological parameters. We also discuss some lessons learnt from J0408-5354 on lensed quasar finding strategies, due to its chromaticity and morphology.

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Title: Discovery of the Lensed Quasar System DES J0408-5354
Author: H. Lin, E. Buckley-Geer, A. Agnello, F. Ostrovski, R. G. McMahon, B. Nord, N. Kuropatkin, D. L. Tucker, T. Treu, J. H. H. Chan, S. H. Suyu, H. T. Diehl, T. Collett, M. S. S. Gill, A. More, A. Amara, M. W. Auger, F. Courbin, C. D. Fassnacht, J. Frieman, P. J. Marshall, G. Meylan, C. E. Rusu, T. M. C. Abbott, F. B. Abdalla, S. Allam, M. Banerji, K. Bechtol, A. Benoit-Lévy, E. Bertin, D. Brooks, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, M. Crocce, C. B. D'Andrea, L. N. da Costa, S. Desai, J. P. Dietrich, T. F. Eifler, D. A. Finley, B. Flaugher, P. Fosalba, J. García-Bellido, E. Gaztanaga, D. W. Gerdes, D. A. Goldstein, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, K. Honscheid, D. J. James, K. Kuehn, O. Lahav, T. S. Li, M. Lima, M. A. G. Maia, et al. (21 additional authors not shown)

We report the discovery and spectroscopic confirmation of the quad-like lensed quasar system DES J0408-5354 found in the Dark Energy Survey (DES) Year 1 (Y1) data. This system was discovered during a search for DES Y1 strong lensing systems using a method that identified candidates as red galaxies with multiple blue neighbours. DES J0408-5354 consists of a central red galaxy surrounded by three bright (i < 20) blue objects and a fourth red object. Subsequent spectroscopic observations using the Gemini South telescope confirmed that the three blue objects are indeed the lensed images of a quasar with redshift z = 2.375, and that the central red object is an early-type lensing galaxy with redshift z = 0.597. DES J0408-5354 is the first quad lensed quasar system to be found in DES and begins to demonstrate the potential of DES to discover and dramatically increase the sample size of these very rare objects.

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