Figure 3 . DES J0446-5126 . The spectra for source images B1 and B2 are shown on the left . The spectrum for A is not shown , but has an emission line consistent with an interpretation as a foreground object . like the others from this confirmed sample , are challenging to model in detail for a precise mass measurement : while there are multiple images of the lensed galaxy , they both occur on one side of the lensing galaxy . We would need well-resolved counterimages for a more precise measurement . The limited resolution of DES images obscures some lensing features , especially for systems with smaller (< 3 ’’) Einstein radii .
In Figure 3 , we see another confirmed lensing system , DES J0446-5126 . Prominent Lymanalpha emission lines in both arcs B1 and B2 occur at the same observed wavelength of 5117 Å , originating in a single source at redshift 3.2 . The object labeled A also has emission lines ( not shown ), which we interpret as [ OII ] 3727 and [ OIII ] 5007 : this must then be a foreground object at redshift 0.17 .
A Warped Future
The spectroscopic observations taken through the Gemini Large and Long program made it possible to confirm six new gravitational lensing systems in DES data .
January 2017 | 2016 Year in Review
We are currently reducing spectroscopic data from the 2nd season of Gemini Large and Long program observations on GMOS South . We are also developing and exploiting automated lens-finding methods , such as ring-finders , arc-finders , and machinelearning algorithms . With these tools we will continue to search for the lenses that can reveal the most about dark energy and the cosmic expansion rate . Large cosmological surveys , like DES and the Large Synoptic Survey Telescope ( LSST ), will have a plethora of data on strong lensing systems . Our main challenges will be not only to obtain complete and pure samples of lenses , but also to find those precious few systems that enable dark energy science .
Brian Nord is a cosmologist and postdoctoral researcher at Fermi National Accelerator Laboratory in Batavia , Illinois . He can be reached at nord @ fnal . gov or on Twitter @ briandnord .
Elizabeth Buckley-Geer is a scientist at Fermi National Accelerator Laboratory . She can be reached at buckley @ fnal . gov .
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