Press Release

Hubble and Keck Team Up to FInd Farthest Known Galaxy in the Universe

By SpaceRef Editor
February 15, 2004
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Hubble and Keck Team Up to FInd Farthest Known Galaxy in the Universe
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An international team of astronomers may have set a new record in
discovering what is the most distant known galaxy in the universe.
Located an estimated 13 billion light-years away, the object is being
viewed at a time only 750 million years after the big bang, when the
universe was barely 5 percent of its current age.

The primeval galaxy was identified by combining the power of NASA’s
Hubble Space Telescope and CARA’s W. M. Keck Telescopes on Mauna Kea in
Hawaii. These great observatories got a boost from the added
magnification of a natural “cosmic gravitational lens” in space that
further amplifies the brightness of the distant object.

The newly discovered galaxy is likely to be a young galaxy shining
during the end of the so-called “Dark Ages” — the period in cosmic
history which ended with the first galaxies and quasars transforming
opaque, molecular hydrogen into the transparent, ionized universe we see
today.

The new galaxy was detected in a long exposure of the nearby cluster of
galaxies Abell 2218, taken with the Advanced Camera for Surveys on board
the Hubble Space Telescope. This cluster is so massive that the light of
distant objects passing through the cluster actually bends and is
amplified, much as a magnifying glass bends and magnifies objects seen
through it. Such natural gravitational ” telescopes” allow astronomers to
see extremely distant and faint objects that could otherwise not be
seen. The extremely faint galaxy is so far away its visible light has
been stretched into infrared wavelengths, making the observations
particularly difficult.

“As we were searching for distant galaxies magnified by Abell 2218, we
detected a pair of strikingly similar images whose arrangement and color
indicate a very distant object,” said astronomer Jean-Paul Kneib
(Observatoire Midi-Pyrenees and Caltech), who is lead author reporting
the discovery in a forthcoming article in the Astrophysical Journal.

Analysis of a sequence of Hubble images indicate the object lies in
between a redshift of 6.6 and 7.1, making it the most distant source
currently known. However, long exposures in the optical and infrared
taken with spectrographs on the 10-meter Keck telescopes suggest that
the object has a redshift towards the upper end of this range, around
redshift 7.

Redshift is a measure of how much the wavelengths of light are shifted
to longer wavelengths. The greater the shift in wavelength toward the
redder regions of the spectrum, the more distant the object is.

“The galaxy we have discovered is extremely faint, and verifying its
distance has been an extraordinarily challenging adventure,” said Dr.
Kneib. “Without the magnification of 25 afforded by the foreground
cluster, this early object could simply not have been identified or
studied in any detail at all with the present telescopes available. Even
with aid of the cosmic lens, the discovery has only been possible by
pushing our current observatories to the limits of their capabilities!”

Using the combination of the high resolution of Hubble and the large
magnification of the cosmic lens, the astronomers estimate that this
object, although very small –only 2,000 light-years across– is forming
stars extremely actively. However, two intriguing properties of the new
source are the apparent lack of the typically bright hydrogen emission
line and its intense ultraviolet light which is much stronger than that
seen in star-forming galaxies closer by.

“The properties of this distant source are very exciting because, if
verified by further study, they could represent the hallmark of a truly
young stellar system that ended the Dark Ages,” added Dr. Richard Ellis,
Steele Professor of Astronomy at Caltech, and a co-author in the
article.

The team is encouraged by the success of their technique and plans to
continue the search for more examples by looking through other cosmic
lenses in the sky. Hubble’s exceptional resolution makes it ideally
suited for such searches.

“Estimating the abundance and characteristic properties of sources at
early times is particularly important in understanding how the universe
reionized itself, thus ending the Dark Ages,” said Mike Santos, a former
Caltech graduate student, now a postdoctoral researcher at the Institute
of Astronomy, Cambridge, UK. “The cosmic lens has given us a first
glimpse into this important epoch. We are now eager to learn more by
finding further examples, although it will no doubt be challenging.”

“We are looking at the first evidence of our ancestors on the
evolutionary tree of the entire universe,” said Dr. Frederic Chaffee,
director of the W. M. Keck Observatory, home to the twin 10-meter Keck
telescopes that confirmed the discovery. “Telescopes are virtual time
machines, allowing our astronomers to look back to the early history of
the cosmos, and these marvelous observations are of the earliest time
yet.”

The Caltech team reporting on the discovery consists of Drs. Jean-Paul
Kneib, Richard S. Ellis, Michael R. Santos and Johan Richard. Drs. Kneib
and Richard also serve the Observatoire Midi-Pyrenees of Toulouse,
France. Dr. Santos also represents the Institute of Astronomy,
Cambridge, UK.

Public funding for this project was provided in part by NASA GSRP grant
NGT5-50339 and NASA STScI grant HST-GO-09452.01-A.

Electronic images and additional information are available at:

For additional information, please contact:

Dr. Jean-Paul Kneib

Observatoire Midi-Pyr=E9n=E9es, France/Caltech, United States

(Phone: 626-395-5928; E-mail: jean-paul.kneib@ast.obs-mip.fr)

Dr. Richard Ellis

Caltech, Pasadena, CA

(Phone: 626-395-2598; Cellular: 626-676-5530;

E-mail rse@astro.caltech.edu)

SpaceRef staff editor.