Hidden Galaxies With New Cosmic Zoom Lenses
ScienceDaily (Nov. 8, 2010)
— Astronomers have discovered a new way of
locating a natural phenomenon that acts like a
zoom lens and allows astronomers to peer at
galaxies in the distant and early Universe. These
results are from the very first data taken as
part of the "Herschel-ATLAS"
project, the largest imaging survey conducted so
far with the European Space Agency's Herschel
Space Observatory, and are published in
the journal Science.
The magnification allows astronomers to see
galaxies otherwise hidden from us when the
Universe was only a few billion years old. This
provides key insights into how galaxies have
changed over the history of the cosmos.
Dr Loretta Dunne from the School of Physics and
Astronomy at The University of Nottingham is
joint-leader of the Herschel-ATLAS survey. Dr
Dunne said: "What we've seen
so far is just the tip of the iceberg. Wide area
surveys are essential for finding these
rare events and since Herschel has only covered
one thirtieth of the entire Herschel-ATLAS area so
expect to discover hundreds of lenses once we have
all the data. Once found, we can probe the
early Universe on the same physical scales as we
can in galaxies next door.
"The data from the area of sky used for this work
has now been released to the astronomical
community and we hope that now astronomers not
directly involved in H-ATLAS will dive into this
data set and exploit the wealth of science which
is bursting to be done with it."
A century ago Albert Einstein showed that gravity
can cause light to bend. The effect is normally
extremely small, and it is only when light passes
close to a very massive object such as a galaxy containing
hundreds of billions of stars that the results
become easily noticeable. When light from a very
distant object passes a galaxy much closer to us,
its path can be bent in such a way that the image
of the distant galaxy is magnified and distorted.
These alignment events are called
"gravitational lenses" and many have been
discovered over recent decades, mainly at visible
and radio wavelengths.
As with a normal glass lens the alignment is
crucial, requiring the position of the lens -- in
this case a galaxy -- to be just right. This is
very rare and astronomers have to rely on chance
alignments, often involving sifting through large
amounts of data from telescopes. Most methods of
searching for gravitational lenses have a very
poor success rate with fewer than one in 10
candidates typically being found to be real.
looks at far-infrared light, which is emitted not
by stars, but by the gas and dust from which they
form. Its panoramic imaging cameras have allowed
astronomers to find examples of these lenses by
scanning large areas of the sky in far-infrared
and sub-millimetre light.
Dr Mattia Negrello, of the Open University and
lead researcher of the study, said: "Our survey of
the sky looks for sources of sub-millimetre light.
The big breakthrough is that
discovered that many of the brightest sources are
being magnified by lenses, which means that we no
longer have to rely on the rather inefficient
methods of finding lenses which are used at
visible and radio wavelengths."
The Herschel-ATLAS images contain thousands of
galaxies, most so far away that the light has
taken billions of years to reach us. Dr Negrello
and his team investigated five surprisingly bright
objects in this small patch of sky. Looking at the
positions of these bright objects with optical
telescopes on the Earth, they found galaxies that
would not normally be bright at the far-infrared
wavelengths observed by Herschel. This led them to
suspect that the galaxies seen in visible light
might be gravitational lenses magnifying much more
distant galaxies seen by Herschel.
To find the true distances to the Herschel
sources, Negrello and his team looked for a
tell-tale signature of molecular gas. Using radio
and sub-millimetre telescopes on the ground, they
showed that this signature implies the galaxies
are being seen as they were when the Universe was
just 2-4 billion years old -- less than a third of
its current age. The galaxies seen by the optical
telescopes are much closer, each ideally
positioned to create a gravitational lens. Dr
Negrello commented that "previous searches for
magnified galaxies have targeted clusters of
galaxies where the huge mass of the cluster makes
the gravitational lensing effect unavoidable.
results show that gravitational lensing is at work
in not just a few, but in all of the distant and
bright galaxies seen by Herschel."
The magnification provided by these cosmic zoom
lenses allows astronomers to study much fainter
galaxies, and in more detail than would otherwise
be possible. They are the key to understanding how
the building blocks of the Universe have changed
since they were in their infancy. Professor Rob
Ivison of the Royal Observatory, Edinburgh, part
of the team that created the images, said "This relatively
simple technique promises to unlock the secrets of
how galaxies like our Milky Way formed and
evolved. Not only does the lensing allow us
to find them very efficiently, but it helps us
peer within them to figure out how the individual
pieces of the jigsaw came together, back in the
mists of time."
Professor Steve Eales from Cardiff University and
the other leader of the survey added: "We can also
use this technique to study the lenses themselves.
This is exciting because 80 per cent of the matter
in the Universe is thought to be dark matter,
which does not absorb, reflect or emit light and
so can't be seen directly with our telescopes.
With the large number of gravitational lenses that
we'll get from our full survey, we'll really be
able to get to grips with this hidden Universe."
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