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National Radio Astronomy Observatory
P.O. Box O
Socorro, NM 87801
http://www.nrao.edu

Contact:
Dave Finley
Public Information Officer, Socorro, NM
(505) 835-7302, dfinley{at}nrao.edu

April 3, 2003

Giant Cosmic Lens Reveals Secrets of Distant Galaxy

Part 1 of 2

Using the National Science Foundation's Very Large Array
(VLA) radio telescope and helped by a gigantic cosmic
lens conveniently provided by nature, an international
team of astronomers has discovered that a young galaxy
had a central disk of gas in which hundreds of new stars
were being born every year -- at a time when the Universe
was only a fraction of its current age.

"This unique look into a very distant, young galaxy gives
us unprecedented insight into the process that produced
both tremendous numbers of stars and supermassive black
holes in forming galaxies," said Chris Carilli, of the
National Radio Astronomy Observatory (NRAO) in Socorro,
NM, leader of the research team. "This work strongly
supports the idea that the stars and the black holes
formed simultaneously," he added. The research was
published in the April 4 issue of Science Express.

The astronomers studied a quasar called PSS J2322+1944,
about 12 billion light-years from Earth. The quasar is
an extremely luminous object powered by the supermassive
black hole at the core of a galaxy. At the distance of
this quasar, the scientists see the object as it was
when the Universe was less than 2 billion years old,
about 15 percent of its current age.

The discovery required a huge assist from nature. To
find the star-forming disk, the astronomers needed to
observe natural radio emission from the carbon monoxide
(CO) molecule, an important component of the gas that
forms stars. However, this molecule emits radio waves
at frequencies much higher than the VLA is capable of
receiving. At PSS J2322+1944's distance of 12 billion
light-years, however, the expansion of the Universe
stretched the radio waves, reducing their frequency.
CO emission at 230 GigaHertz was shifted to 45
GigaHertz, within the VLA's range.

That alone was not enough. The distance that made it
possible to receive the radio waves from the quasar
also meant that the object was too far away for the
VLA to discern the detail required to show the disk.
Once again, nature stepped in to help, providing
another galaxy directly between the quasar and Earth
to form a gravitational lens.

"What we needed wasn't just any old gravitational lens,
but a nearly-perfect alignment of the distant quasar,
mid-distance galaxy, and Earth -- and that's what we
got," said Geraint Lewis of the University of Sydney
in Australia, another member of the team. With such a
perfect alignment, the quasar image was distorted into
a ring, called an "Einstein Ring." The VLA images were
the first to show the Einstein Ring of PSS J2322+1944.

"We never would have seen the disk of CO gas near the
center of this galaxy without the gravitational lens,"
said Carilli. "The lens boosted the signal and
magnified the image to reveal the disk's structure in
unprecedented detail," he added.

For several years, astronomers have noted that the
masses of black holes are directly proportional to
the sizes of central bulges of stars in galaxies. This
led to the speculation that formation of the black
holes and of the stars are somehow related to each
other. Scientists hypothesized that gas being drawn
towards a galaxy's central black hole is the same gas
from which large numbers of stars are forming.

Studies of more-nearby galaxies supported such
speculation, but the question remained whether the
idea could be applied to the very early Universe,
when the first galaxies and black holes formed.

"This new observation gives strong support to the idea
that large numbers of stars were forming in young
galaxies at the same time that their central black
holes were pulling in additional mass," said Pierre
Cox, of the Institute for Space Astrophysics of the
University of Paris.

The astronomers believe that galaxies in the early
Universe were frequently disrupted by nearby encounters
with other galaxies, "feeding" the central black hole
with gas. The gas formed an extensive, spinning disk
around the galaxy's center, some of it eventually
falling into the black hole and some of it forming
new stars.

In PSS J2322+1944, the astronomers believe that new
stars with a total mass equal to some 900 times that
of the Sun were forming in the 13,000-light-year-
diameter disk every year. At that rate, the scientists
say, most of the stars in a large elliptical galaxy
could form in only about 100 million years.

PSS J2322+1944 is one of the most luminous quasars
in the Universe. It was first discovered by George
Djorgovski and his collaborators from the California
Institute of Technology (Caltech), using the digitized
Palomar Observatory Sky Survey. Later studies led by
Cox and Alain Omont of the Astrophysical Institute of
Paris using the IRAM millimeter-wave facilities in
Europe (the 30-meter telescope and the Plateau de Bure
Interferometer) showed that it had a huge reservoir of
dust and molecular gas, the fuel for star formation.
Optical observation at the W.M. Keck Observatory
in Hawaii showed a double image that indicated
gravitational lensing. All these factors, the
scientists said, made it an ideal candidate for study
with the VLA.

 - Continued -

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