GeminiFocus July 2016 | Page 9

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. cise 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 GLLP made it possible to confirm six new gravitational lensing systems in DES data. We are currently reducing spectroscopic data from the 2nd season of GLLP July 2016 observations on GMOS South. We are also developing and exploiting automated lensfinding methods, such as ring-finders, arcfinders, and machine-learning 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 [email protected] or on Twitter @briandnord. Elizabeth Buckley-Geer is a scientist at Fermi National Accelerator Laboratory. She can be reached at [email protected]. GeminiFocus 7