Finding and confirming candidates are the
first steps in measuring cosmic structure and
dark energy with strong lenses. The results
will help us to understand why the Universe
is accelerating and not being slowed by the
mass it contains.
When Space Gets Warped
One maxim of Einstein’s Theory of General
Relativity is that space-time — the concept
that space and time are one — tells energy
how to move, and energy tells space-time
how to curve. Gravitational lensing demonstrates both of these concepts: the path
of light traveling from a distant object (like
a galaxy) is deflected by a depression in the
fabric of space-time caused by a massive
object nearer to us. The more massive this
intervening lensing object, the larger the
crater, and the more distorted the observed
image of the distant source galaxy.
Gravitational lenses act like terrestrial lenses
made of plastic or glass, bending light in
ways we can model well with geometric optics; the equations have multiple simultane-
ous solutions, which describe the different
paths light can take from a single source, as
well as the amount of magnification in the
lensed image. A single source galaxy can appear highly magnified and have multiple images — both telltale signatures of a strong
lensing system.
What Can Strong Lenses Tell Us
about the Universe?
With strong gravitational lensing we can examine in detail galaxies normally too faint
to observe. The observations also provide
an avenue for studying galaxy evolution at
epochs earlier in the Universe than would
be available otherwise. The total lensing
mass and its spatial distribution dictate the
morphologies of lensed images. By measuring the amount and type of distortion of the
source image, we can learn more about the
mass distribution (including that due to dark
matter) in the lensing galaxies or clusters.
Moreover, particular configurations of lenses can help constrain dark energy models.
In systems with two or more source galaxies
Figure 1.
Color images of six
strong lenses confirmed
with Gemini South
spectroscopic follow-up:
a) DES J0221-0646,
b) DES J0250-0008,
c) DES J0329-2820,
d) DES J0330-5228,
e) DES J0446-5126, f)
DES J2336-5352. Each
of these systems is a
galaxy group or richer
cluster, but just one or
a few galaxies near the
center of the cluster
cause most of the
lensing.
(All figures reproduced
from Nord et al., 2016.)
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GeminiFocus
July 2016