News: Astronomers Find One of the Youngest and Brightest Galaxies in the Early Universe.

Astronomers Find One of the Youngest and Brightest Galaxies in the
Early Universe

http://hubblesite.org/newscenter/archive/releases/2008/08/full/

News Release Number: STScI-2008-08
February 12, 2008 09:00 AM (EST)

NASA's Hubble and Spitzer space telescopes, with a boost from a
natural "zoom lens," have uncovered what may be one of the youngest
and brightest galaxies ever seen in the middle of the cosmic "dark
ages," just 700 million years after the beginning of our universe.

The detailed images from Hubble's Near Infrared Camera and
Multi-Object Spectrometer (NICMOS) reveal an infant galaxy, dubbed
A1689-zD1, undergoing a firestorm of star birth during the dark ages,
a time shortly after the Big Bang but before the first stars reheated
the cold, dark universe. Images from NASA's Spitzer Space Telescope's
Infrared Array Camera provided strong additional evidence that it was
a young star- forming galaxy in the dark ages.

"We certainly were surprised to find such a bright young galaxy 12.8
billion years in the past," said astronomer Garth Illingworth of the
University of California, Santa Cruz, and a member of the research
team. "This is the most detailed look to date at an object so far back
in time."

"The Hubble images yield insight into the galaxy's structure that we
cannot get with any other telescope," added astronomer Rychard Bouwens
of the University of California, Santa Cruz, one of the co-discoverers
of this galaxy.

The new images should offer insights into the formative years of
galaxy birth and evolution and yield information on the types of
objects that may have contributed to ending the dark ages. The faraway
galaxy also is an ideal target for Hubble's successor, the James Webb
Space Telescope (JWST), scheduled to launch in 2013.

During its lifetime, the Hubble telescope has peered ever farther back
in time, viewing galaxies at successively younger stages of evolution.
These snapshots have helped astronomers create a scrapbook of galaxies
from infancy to adulthood. The new Hubble and Spitzer images of
A1689-zD1 show a time when galaxies were in their infancy.

Current theory holds that the dark ages began about 400,000 years
after the Big Bang, as matter in the expanding universe cooled and
formed clouds of cold hydrogen. These cold clouds pervaded the
universe like a thick fog.

At some point during this era, stars and galaxies started to form.
Their collective light reheated the foggy, cold hydrogen, ending the
dark ages about a billion years after the Big Bang.

"This galaxy presumably is one of the many galaxies that helped end
the dark ages," said astronomer Larry Bradley of Johns Hopkins
University in Baltimore, Md., and leader of the study. "Astronomers
are fairly certain that high-energy objects such as quasars did not
provide enough energy to end the dark ages of the universe. But many
young star- forming galaxies may have produced enough energy to end
it."

The galaxy is so far away it did not appear in images taken with
Hubble's Advanced Camera for Surveys, because its light is stretched
to invisible infrared wavelengths by the universe's expansion. It took
Hubble's NICMOS, Spitzer, and a trick of nature called gravitational
lensing to see the faraway galaxy.

The astronomers used a relatively nearby massive cluster of galaxies
known as Abell 1689, roughly 2.2 billion light-years away, to magnify
the light from the more distant galaxy directly behind it. This
natural telescope is called a gravitational lens.

Though the diffuse light of the faraway object is nearly impossible to
see, gravitational lensing has increased its brightness by nearly 10
times, making it bright enough for Hubble and Spitzer to detect. A
telltale sign of the lensing is the smearing of the images of galaxies
behind Abell 1689 into arcs by the gravitational warping of space by
the intervening galaxy cluster.

The images reveal bright, dense clumps of hundreds of millions of
massive stars in a compact region about 2,000 light-years across,
which is only a fraction of the width of our Milky Way Galaxy. This
type of galaxy is not uncommon in the early universe, when the bulk of
star formation was taking place, Bradley and Illingworth said.

Spitzer's images show that the galaxy's mass is typical to that of
galaxies in the early universe. Its mass is equivalent to several
billions of stars like our Sun, or just a tiny fraction of the mass of
the Milky Way.

"This observation confirms previous Hubble studies that star birth
happens in very tiny regions compared with the size of the final
galaxy," Illingworth said.

Even with the increased magnification from the gravitational lens,
Hubble's sharp "eye" can only see knots of the brightest, heftiest
stars in the galaxy. The telescope cannot pinpoint fainter, lower-mass
stars, individual stars, or the material surrounding the star-
birthing region. To see those things, astronomers will need the
infrared capabilities of NASA's JWST. The planned infrared observatory
will have a mirror about seven times the area of Hubble's primary
mirror and will collect more light from faint galaxies. JWST also will
be able to view even more remote galaxies whose light has been
stretched deep into infrared wavelengths that are out of the reach of
NICMOS.

"This galaxy will certainly be one of the first objects that will be
observed by JWST," said team member Holland Ford of Johns Hopkins
University. "This galaxy is so bright that JWST will see its detailed
structure. This object is a pathfinder for JWST for deciphering what
is happening in young galaxies."

The astronomers noted that the faraway galaxy also would be an ideal
target for the Atacama Large Millimeter Array (ALMA), which, when
completed in 2012, will be the most powerful radio telescope in the
world. "ALMA and JWST working together would be an ideal combination
to really understand this galaxy," Illingworth said, noting that
"JWST's images and ALMA's measurement of the gas motions will provide
revolutionary insights into the very youngest galaxies."

The astronomers will conduct follow-up observations with infrared
spectroscopy to confirm the galaxy's distance using the Keck telescope
atop Mauna Kea in Hawaii.

The results will be published in the Astrophysical Journal.

--
Bob.

.

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