Mining for cosmic treasures with GEMS (Forwarded)

FOR RELEASE: 9:30am EST, 8 January 2004

MINING FOR COSMIC TREASURES WITH GEMS

ATLANTA -- The largest contiguous color image taken with the Hubble Space
Telescope was unveiled today by an international team of astronomers at the
American Astronomical Society meeting in Atlanta, Georgia. Dr. Eric F. Bell of
the Max-Planck-Institute for Astronomy in Heidelberg, Germany, and Dr. Shardha
Jogee of the Space Telescope Science Institute in Baltimore, Maryland presented
an image in the constellation Fornax equal to the apparent size of the full moon
containing more than 40,000 galaxies. The astronomers, members of a large team
called the GEMS consortium and led by Dr. Hans-Walter Rix, Director of the
Max-Planck-Institute for Astronomy, said the image will help them understand how
large galaxies, like the Milky Way, evolved over the last nine billion years,
about 2/3 the age of the universe. GEMS is an acronym for Galaxy Evolution from
Morphology and Spectral energy distributions.

To construct the image, the team stitched together 78 separate exposures from
Hubble's Advanced Camera for Surveys. "It's like making a big picture of a
mountain range by pasting together individual pictures of each mountain -- we
have done exactly the same thing, only with the Hubble Space Telescope", said
Dr. Daniel H. McIntosh, a researcher at the University of Massachusetts in
Amherst, Massachusetts.

The main advantage of GEMS is its large area. "This is the largest color image
ever taken by HST", continues McIntosh. "Because galaxies clump together in
space, smaller images may accidentally land on unusual patches. For example, a
picture of the USA at night shows bright areas near the cities and dark areas in
the mountains, forest, and farmlands. To understand the population of the
United States, we would need an image covering both the rare, bright cities and
the dark but sparsely-populated farmland and wilderness. Furthermore, galaxies,
like people are incredibly diverse. Only by having images of a large sample of
galaxies can one explore the huge diversity of galaxy types, sizes and shapes,
as well as discovering important but very brief episodes in their lives."

The team chose an area in which they already knew the distances to nearly ten
thousand galaxies. Because of the expansion of the Universe, more distant
galaxies are moving away from us faster than nearby galaxies. Astronomers use
the Doppler shift of the galaxies' light to measure this movement and compute
the distance. And because the light from distant galaxies takes longer to reach
Earth than that from the nearby objects, we see distant galaxies as they were in
the past, giving astronomers a kind of cosmic 'time machine.' GEMS can see back
accurately about 9 billion years, 4.5 billion years before the Sun and the Earth
formed.

Dr. Christian Wolf of the University of Oxford and Dr. Klaus Meisenheimer of the
Max-Planck-Institute for Astronomy led a team to measure the distances to ten
thousand galaxies in GEMS with accuracies of a few percent. "This is the first
time that astronomers have had such a large sample of galaxies with accurate
distances and exquisite HST data", said Wolf. He continues, "With these
distances and the exquisite images, astronomers can investigate how the sizes
and structures of galaxies evolve over the last 9 billion years." For instance,
one of the questions addressed by GEMS is the evolution of stellar bars --
majestic elongated stellar concentrations which shape galaxy evolution by
driving gas towards the central regions of galaxies, often igniting spectacular
bursts of star formation. Although the majority of present-day spiral galaxies
host stellar bars, including our own Galaxy, little is known about when and how
bars formed at earlier epochs.

One of the many goals of GEMS is to investigate how galaxy interactions impact
galaxy evolution. Interacting galaxies exert strong gravitational forces and
shocks on each other, induce dramatic morphological transformations, and may
even merge into a final product which is vastly different from the progenitors.
"With GEMS, we identify interacting and merging galaxies over the last 9
billion years by capturing their tell-tale strongly disturbed morphologies:
double bright nuclei, stellar tidal tails flung out over thousands of light
years, and highly asymmetric star formation", says Jogee. Interactions may also
play an important role in feeding gas to huge black holes in the centers of
massive galaxies, 'activating' the nucleus into releasing prodigious amounts of
energy. GEMS can bring valuable insights into the nature of galaxies hosting
such active nuclei. "Furthermore, our current understanding of the physics of
galaxy interactions is still pretty uncertain, and good observations of how
frequently galaxies merge at different times in the Universe's history would be
a really important part of this puzzle," said Dr. Rachel S. Somerville, a staff
astronomer at the Space Telescope Science Institute in Baltimore, Maryland.
First indications are that galaxy interactions are much more common in the past
than they are today. "Most massive galaxies are simply aging now, fading slowly
into obscurity", said Rix.

Another focus of GEMS is to explore the leftovers of particularly violent galaxy
mergers -- watermelon-shaped galaxies called elliptical galaxies. "With GEMS,
we have proven for the first time that there are more elliptical galaxies today
than there were in the past", explains Bell. "This is exciting first evidence
for a merger origin of at least some elliptical galaxies."

Authors:

Eric F. Bell, Max-Planck-Institute for Astronomy
Konigstuhl 17, D-69117, Heidelberg, Germany
, +49 6221 528 263

Shardha Jogee, Space Telescope Science Institute
3700 San Martin Drive, Baltimore MD 21218
, (410) 338 4349

Hans-Walter Rix, Max-Planck-Institute for Astronomy
, +49 6221 528 210

Marco Barden, Max-Planck-Institute for Astronomy


Steven V. W. Beckwith, Space Telescope Science Institute


Andrea Borch, Max-Planck-Institute for Astronomy


John A. R. Caldwell, Space Telescope Science Institute


Boris Haeussler, Max-Planck-Institute for Astronomy


Knud Jahnke, Astrophysikalisches Institut Potsdam
An der Sternwarte 16, D-14482 Potsdam, Germany


Daniel H. McIntosh, Astronomy Department
University of Massachusetts, Amherst, MA 01003


Klaus Meisenheimer, Max-Planck-Institute for Astronomy


Chien Y. Peng, Steward Observatory
University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721


Sebastian F. Sanchez, Astrophysikalisches Institut Potsdam


Rachel S. Somerville, Space Telescope Science Institute


Lutz Wisotzki, Astrophysikalisches Institut Potsdam


Christian Wolf, Astrophysics Department
University of Oxford
Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK


Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at
the Space Telescope Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555.
These observations are associated with program #9500. This research was
supported by the DFG (German Research Foundation), the Max Planck Society, the
European Union Human Potential Program, the National Science Foundation and the
National Aeronautics and Space Administration.

Electronic versions of the figures are available at:

http://www.mpia-hd.mpg.de/homes/bell...ase/press.html

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