reliable for the more remote galaxies likely
to be lensed.
To measure redshifts, we look for specific
features, like emission or absorption lines, in
the spectra of source galaxies: the higher the
redshift, the further these features shift from
their rest wavelength. We use the R150 grating in conjunction with the GG455 filter to
obtain spectra with a wavelength coverage
of 4500-10000 angstroms (Å). For the sources that we expect to be late-type emission
line galaxies, this would allow us, in many
cases, to detect [OII]3727 to z ~ 1.7, H-beta
to z ~ 1.0, and Lyman-alpha in the range 2.7
< z < 7.2. We use the B600 grating to obtain
spectral coverage of 3250-6250 Å, which
would allow us to detect sources with z > 2.0
that emit Lyman-alpha.
We acquired spectroscopic data for 21 of
the 53 systems: 17 were observed at Gemini South (taken through the Gemini Large
and Long Program), and five were observed
with the Inamori Magellan Areal Camera
and Spectrograph at the Magellan/Baade
telescope (with an overlap of one system).
We confirmed six strong lensing candidates
with Gemini South, rejected two, and the
status of 13 remain inconclusive. For the rejected systems, we found that the putative
source galaxies were actually foreground
galaxies. The inconclusive systems may have
spectral features at higher wavelengths,
which would require the use of other instruments or telescopes.
Let’s look in detail at some of the confirmed
systems. Figure 2 shows spectra of the source
galaxy images A1 and A2, along with images
of the lensing system DES J0221- 0646. Taking into account the absence of other spectral features, we assign the features at 4535 Å
to be Lyman-alpha, which gives a redshift of
~ 2.752, placing it behind the redshift 0.672
lensing galaxy.
The middle color image of Figure 2 shows
an Einstein radius estimated by manually fitting a circle that passes through the spectroscopically confirmed source images, where
the center is chosen to be the arcs’ center of
curvature. With these radii, we estimated the
mass enclosed within that circle. This system,
like the others from this confirmed sample,
are challenging to model in detail for a pre-
Fi