Astronomers Claim to Find the Most Distant Known Galaxies (Forwarded)

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CONTACTS:

Richard Ellis
Astronomy Department, California Institute of Technology
Pasadena CA 91125
E-mail: rse @ astro.caltech.edu

Dan Stark
Astronomy Department, California Institute of Technology
Pasadena CA 91125
E-mail: dps @ astro.caltech.edu

Jean-Paul Kneib
Laboratoire d'Astrophysique de Marseille
Traverse du Siphon - B.P.8 F-13376 Marseille Cedex 12
E-mail: jean-paul.kneib @ oamp.fr

Jill Perry
Caltech Media Relations, (626) 395-3226

Robert Massey
Royal Astronomical Society
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July 10, 2007

Astronomers Claim to Find the Most Distant Known Galaxies

PASADENA, Calif. -- Using natural "gravitational lenses," an international
team of astronomers claim to have found the first traces of a population
of the most distant galaxies yet seen -- the light we see from them today
left more than 13 billion years ago, when the universe was just 500
million years old.

Team leader Richard Ellis, the Steele Family Professor of Astronomy at the
California Institute of Technology, will present images of these faint and
distant objects in his talk on July 11 at the "From IRAS to Herschel and
Planck" conference at the Geological Society in London. The meeting is
being held to celebrate the 65th birthday of Royal Astronomical Society
President Professor Michael Rowan-Robinson.

When light from very distant bodies passes through the gravitational field
of much nearer massive objects, it bends in an effect known as
"gravitational lensing." In a pioneering technique, the Caltech-led group
used massive clusters of galaxies -- the best example of natural
gravitational lenses -- in a series of campaigns to locate progressively
more distant systems that would not be detected in normal surveys. The
team found the galaxies using the 10-meter Keck II telescope, sited atop
Mauna Kea on the Big Island of Hawaii.

Ellis explains, "Gravitational lensing is the magnification of distant
sources by foreground structures. By looking through carefully selected
clusters, we have located six star-forming galaxies seen at unprecedented
distances, corresponding to a time when the universe was only 500 million
years old, or less than four percent of its present age."

It is thought that when the universe was 300,000 years old it entered a
period when no stars were shining. Cosmologists refer to this phase of
cosmic history as the "Dark Ages." Pinpointing the moment of "cosmic dawn"
when the first stars and galaxies began to shine and the Dark Ages ended
is a major observational quest and provides the motivation for building
future powerful telescopes such as the Caltech's Thirty Meter Telescope,
and the space-borne James Webb Telescope.

The new survey is the culmination of three years' painstaking observations
which represent the thesis of Caltech graduate student Dan Stark. "Using
Keck II, we have detected six faint star-forming galaxies whose signal has
been boosted about 20 times by the magnifying effect of a foreground
cluster. That we should find so many distant galaxies in our small survey
area suggests they are very numerous indeed. We estimate the combined
radiation output of this population could be sufficient to break apart
(ionize) the hydrogen atoms in space at that time, thereby ending the Dark
Ages," said Stark.

Proving definitively that each of the six objects is unambiguously at
these enormous distances (and hence being viewed at such early times) is
hard, even with the most powerful instruments. "As with all work at the
frontiers, skeptics may wish to see further proof that the objects we are
detecting with Keck are really so distant," confessed Ellis. However, in
addition to numerous checks the team has made (described in their
published scientific article) following their initial discovery a year
ago, Ellis and Stark point to supporting evidence from galaxies containing
old stars that are seen when the universe was just a bit older.

"We can infer the universe had a lot of star formation at these early
times from Spitzer Space Telescope measurements of larger galaxies seen
when the universe was about 300 to 500 million years older," explains
Stark. "These galaxies show the tell-tale sign of old stars (and were
described in earlier work by Ellis and Stark with UK scientist Andrew
Bunker). To produce these old stars requires significant earlier activity,
most likely in the fainter star-forming galaxies we have now seen."

Also associated with the program is Caltech postdoctoral scholar Johan
Richard, who is leading a similar, but independent, survey of magnified
galaxies detected with the Hubble and Spitzer space telescopes. Although
that work is not yet complete, preliminary findings support the
conclusions of the Keck II survey. European collaborators include
Jean-Paul Kneib of the Laboratory of Astrophysics at Marseilles, and
Graham Smith at the University of Birmingham.

FURTHER INFORMATION

Details of the conference can be found at:
http://www.ras.org.uk/
http://astro.ic.ac.uk/Research/herschel_conference/

IMAGES

Images of the new galaxies and a description of the technique used can be
seen at:
http://www.astro.caltech.edu/~johan/cosmic_dawn/

SCIENTIFIC ARTICLE

The refereed scientific article can be found on the Astrophysical Journal
website:
http://www.journals.uchicago.edu/ApJ/home.html
(Volume 663, pages 10-28, 2007)