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].
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