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Galaxy survey focuses on universe's 'pre-teen' years (Forwarded)



 
 
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Old March 7th 07, 05:56 PM posted to sci.space.news
Andrew Yee[_1_]
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Default Galaxy survey focuses on universe's 'pre-teen' years (Forwarded)

Media Relations
University of California-Berkeley

Media Contacts:
Robert Sanders
(510) 643-6998 / (510) 642-3734

Additional Resources:
Jeffrey Newman, Lawerence Berkeley Lab
(510) 390-2450

Raja Guhathakurta, UC Santa Cruz
(831) 459-5169

Marc Davis, UC Berkeley
(510) 642-5156

FOR IMMEDIATE RELEASE: Tuesday, March 06, 2007

Galaxy survey focuses on universe's 'pre-teen' years

A massive project to generate an all-color map of the galaxies in a small
area of sky, utilizing four satellite telescopes and four ground-based
telescopes, is yielding new information about the universe's "pre-teen"
years and the early evolution of galaxies and galaxy clusters.

Called the All-wavelength Extended Groth Strip International Survey (AEGIS),
the five-year project involved the cooperation of more than 50 researchers
from around the world observing the same small region of sky in the radio,
infrared, visible, ultraviolet and X-ray regions of the electromagnetic
spectrum. The target area, called the Extended Groth Strip, covers an area
the width of two full moons that is a hop, skip and a jump from the end of
the Big Dipper's handle.

"The goal was to study the universe as it was when it was about half as old
as it is at present," said team leader Marc Davis, professor of physics and
astronomy at the University of California, Berkeley. "We've gotten such
fabulous data; it just blows your socks off."

A total of 19 papers based on the Groth Strip survey have been accepted for
publication in the Astrophysical Journal (ApJ) Letters, and will appear in a
special issue in early spring. All currently are posted online at
http://aegis.ucolick.org/publications.html#apjl2006

Combined with spectra of these galaxies obtained through the W. M. Keck
Telescope in Hawaii as part of the DEEP2 Galaxy Redshift Survey, the dataset
will be an invaluable resource for astronomers, he said. Among the
discoveries so far are a giant red galaxy with two black holes at its core;
several new gravitational lenses -- that is, galaxies whose gravity bends
the light from background galaxies into multiple images; and a rogues'
gallery of weird galaxies that astronomers will be busy trying to explain
for decades.

To the naked eye, the Extended Groth Strip, named for Princeton University
physicist Edward Groth, is empty, but the AEGIS survey pinpointed more than
150,000 galaxies in the strip. A panoramic mosaic of Hubble Space Telescope
images released today (Tuesday, March 6) provides detailed, color images of
at least 50,000 galaxies in part of this area. The AEGIS survey is focused
on studying galaxies up to 9 billion years back in time -- more than half
way to the birth of the universe 13.7 billion years ago. It covers a period
when galaxies were settling down after an early phase of rapid star
formation.

"We're studying a key epoch when galaxies appear to be taking on their final
mature forms," said Sandra Faber, professor of astronomy at UC Santa Cruz.
"It's like seeing people at the age of 10 -- they are not exactly infants,
but they differ substantially from adults. We are watching galaxies grow
up."

In a summary paper now posted online in ApJ Letters, Davis and his
colleagues note that AEGIS is providing a unique combination of deep,
intensive observations over a wide area, yielding large samples even of rare
types of galaxies. They contrast their work with the Sloan Digital Sky
Survey, which has observed the local universe in great detail, but focuses
on only the last 2 billion years of cosmic evolution.

"We have looked at this patch of sky with every possible telescope, at
wavelengths covering nine orders of magnitude -- that's a wavelength range
of a billion, compared to the ability of our eyes to see a range of two,"
said cosmologist Jeffrey A. Newman, a Hubble Fellow at Lawrence Berkeley
National Laboratory. "Each provides a little piece of the puzzle of how
galaxies evolve."

"As of this time, there is no other region this large on the sky that has
been looked at so deeply in so many different wavelengths," Faber said.
"This is the first truly panchromatic look at the universe more than halfway
back in time."

According to Newman, the Hubble Space Telescope images reveal a time when
galaxies were starting to reach maturity.

"We see a wide diversity of galaxies. Some are beautiful spirals or massive
elliptical galaxies like those seen in the nearby universe, but others look
like random assemblages of material, the leftovers from violent mergers of
young galaxies. These resemble some of the most distant, youngest galaxies
observed," he said.

AEGIS provides many windows on this time of transition. Ultraviolet and
far-infrared light from newly-born stars, observed by the GALaxy Evolution
eXplorer (GALEX) and the Spitzer Space Telescope, respectively, shows that
stars were being formed at a much higher rate than today. Mid- and
near-infrared light measures the total mass of the stars in each galaxy,
allowing astronomers to see how galaxies grow larger over time, while X-ray
and radio observations by the Chandra Space Telescope and the Very Large
Array in New Mexico, respectively, can reveal the presence of powerful black
holes at galaxies' centers.

A linchpin for AEGIS studies, Davis said, is the DEEP2 Redshift Survey,
which measures many properties of a galaxy -- its mass, the rate at which it
is forming stars, and more -- while simultaneously determining how far away
it is, and, hence, how far back in time we're observing. The large number of
objects surveyed by DEEP2 in the Groth Strip -- 14,000 to date, though the
completed survey should include nearly 18,000 galaxies -- allows astronomers
to see trends as the universe ages. The data clearly show that the galaxies
at the far edge of the survey, around 9 billion years ago, are noticeably
different from those at the near, 7 billion-year edge of the survey, which
look more like "normal" galaxies today.

Because of the relatively large cosmic volume covered, astronomers are able
to find even rare objects, such as galaxies with two separate black holes at
their centers, that can help reveal the hidden physics of galaxy formation
and evolution.

The new survey also revealed two new lensing galaxies, an already known
Einstein Cross -- a case where a massive galaxy has split the light from a
background galaxy into four arcs -- and four possible lenses. According to
Puragra "Raja" Guhathakurta of UC Santa Cruz's Lick Observatory, astronomers
can apply Einstein's theory of general relativity to calculate the masses of
lensing galaxies given their spectra and the observed bending of starlight.

The AEGIS data were supplied by the orbiting Hubble (optical), Chandra
(X-ray), GALEX (ultraviolet) and Spitzer (infrared) telescopes, all operated
by the National Aeronautics and Space Administration (NASA). The
Canada-France-Hawaii Telescope atop Mauna Kea contributed optical data;
California's Palomar Telescope provided near-infrared data; the Very Large
Array in New Mexico provided radio observations; and the DEep Imaging
Multi-Object Spectrograph (DEIMOS) instrument on the 10-meter Keck II
telescope provided spectra of the galaxies. The full set of AEGIS data are
planned to be released to the public in August 2007.

The AEGIS collaboration has been supported by the National Science
Foundation and NASA. The DEEP2 survey, funded by NSF and led by Davis and
Faber, is a collaboration between astronomers at UC Berkeley, UC Santa Cruz
and the University of Hawaii.

SIDEBAR

Binary black holes hint of past galactic merger

Many astronomers suspect that all galaxies have a massive black hole at the
center, though only those with matter falling into them are visible,
becoming what is referred to as an active galactic nucleus. Quasars are
among the brightest examples of these objects. When two galaxies merge,
their central black holes should end up together at the core, eventually
spiraling into one another. However, while galaxy mergers have been observed
in abundance, few cases of galaxies with multiple massive black holes are
known. Such objects may be difficult to find, as both black holes must be
actively accreting matter for them to be visible.

Plumbing the DEEP2 data, UC Berkeley graduate student Brian Gerke discovered
a double black hole in a galaxy about 6 billion light years away, at z=0.7.
He confirmed the presence of an active galactic nucleus with AEGIS
observations from the Chandra X-ray satellite. The two black holes are about
4,000 light years apart, one of them 500,000 and the other 5 million times
the mass of the Sun. Their separation is small compared to the object's
distance from us; so that, even in high-resolution images from the Hubble
Space Telescope, they are blurred together at the center of a fairly normal
looking, elliptical galaxy.

Evidently, he said, what we are seeing is the combination of two galaxies
that merged hundreds of millions of years earlier. Since the merger, the
central black holes have spiraled toward one another to the distance we now
observe. Though other dual black holes have been seen closer to Earth
(notably NGC6240), they generally are visible only in X-ray or radio. This
pair is visible in the optical. This is apparently because the host galaxy
was formed from the combination of two "red and dead," elliptical or
lenticular galaxies, which contain little of the obscuring dust that
enshrouds the centers of mergers of star-forming galaxies (these galaxies
are commonly referred to as "red and dead" because their star formation
ceased at least a billion years ago, so their short-lived blue stars have
all died).

There has been indirect evidence from studies of the galaxy population as a
whole that mergers of red galaxies must have occurred in the distant past,
but most tracers of these mergers are undetectable at large distances,
making this object valuable for understanding galaxy evolution.

"This tells us where massive ellipticals come from -- the merger of smaller
galaxies," Gerke said.

# # #

Web Links to additional Information:

For color images and information about the AEGIS project, plus summaries of
the AEGIS papers in ApJ Letters, go to
http://aegis.ucolick.org

For Hubble Space Telescope images and video of the Extended Groth Strip,
link to
http://hubblesite.org/news/2007/06

[NOTE: Images supporting this release are available at
http://www.berkeley.edu/news/media/r...06_aegis.shtml ]
 




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