EMBARGOED For Release: 9:30 a.m., CST, Thursday, January 10, 2008
Contact:
Dave Finley, Public Information Officer
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New VLA Images Unlocking Galactic Mysteries
Astronomers have produced a scientific gold mine of detailed, high-quality images of nearby galaxies that is yielding important new
insights into many aspects of galaxies, including their complex
structures, how they form stars, the motions of gas in the galaxies,
the relationship of "normal" matter to unseen "dark matter," and
many others.
An international team of scientists used more than 500 hours of
observations with the National Science Foundation's Very Large Array
(VLA) radio telescope to produce detailed sets of images of 34 galaxies at
distances from 6 to 50 million light-years from Earth. Their project,
called The HI Nearby Galaxy Survey, or THINGS, required two years to
produce nearly one TeraByte of data. HI ("H-one") is an astronomical
term for atomic hydrogen gas. The astronomers presented their initial
findings to the American Astronomical Society's (AAS) meeting in Austin,
Texas.
"Studying the radio waves emitted by atomic hydrogen gas in galaxies
is an extremely powerful way to learn what's going on in nearby
galaxies. The THINGS survey uses that tool to provide sets of images
of the highest quality and sensitivity for a substantial sample of
galaxies of different types," said Fabian Walter, of the Max-Planck
Institute for Astronomy in Heidelberg, Germany.
Dwarf galaxy IC2574, left, and spiral galaxy M74, in THINGS images. Credit: Walter et al., NRAO/AUI/NSF
Click images for high-resolution files (33 KB & 25 KB)
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Most of the galaxies studied in the THINGS survey also have been
observed at other wavelengths, including Spitzer space telescope infrared
images and GALEX ultraviolet images. This combination provides an
unprecedented resource for unravelling the mystery of how a galaxy's
gaseous material influences its overall evolution.
Analysis of THINGS data already has yielded numerous scientific payoffs.
For example, one study has shed new light on astronomers' understanding of
the gas-density threshold required to start the process of star formation.
"Using the data from THINGS in combination with observations from NASA's
space telescopes has allowed us to investigate how the processes leading
to star formation differ in big spiral galaxies like our own and much
smaller, dwarf galaxies," said Adam Leroy and Frank Bigiel of the
Max-Planck Insitute for Astronomy at the Austin AAS meeting.
Because atomic hydrogen emits radio waves at a specific frequency,
astronomers can measure motions of the gas by noting the Doppler shift
in frequency caused by those motions. "Because the THINGS images are
highly detailed, we have been able to measure both the rotational
motion of the galaxies and non-circular random motions within the
galaxies," noted Erwin de Blok of the University of Cape Town, South
Africa.
The motion measurements are providing new information about the
mysterious, unseen "dark matter" in the galaxies. "The non-circular
motions revealed by the THINGS observations, turn out to be too small
to solve a long-standing problem in cosmology, namely the inability of
state-of-the-art computer simulations to describe the distribution of
dark matter in disk galaxies. It was thought that random motions
could explain that inability, but our data show otherwise," de Blok
explained.
The THINGS images revealed what Elias Brinks of the University of
Hertfordshire, UK, called a "stunning complexity of structures in the
tenuous interstellar medium of the galaxies." These structures include
large shells and "bubbles," presumably caused by multiple supernova
explosions of massive stars. Analyzing the detail of these complex
structures will help astronomers better understand the differences in
star formation processes in the varied types of galaxies.
Even such a simple question such as how big are the disks of gas in
spiral galaxies had largely eluded astronomers previously. "The
quality and sensitivity of the THINGS images has allowed us to see the
actual edges of these disks in a large sample of galaxies," said
Brinks.
The new survey also showed a fundamental difference between the nearby
galaxies -- part of the "current" Universe, and far more distant galaxies,
seen as they were when the Universe was much younger. "It appears that
the gas in the galaxies in the early Universe is much more 'stirred up,'
possibly because galaxies were colliding more frequently then and there
was more intense star formation causing material outflows and stellar
winds," explained Martin Zwaan of the European Southern Observatory. The
information about gas in the more distant galaxies came through
non-imaging analysis.
These discoveries, the scientists predict, are only the tip of the
iceberg. "This survey produced a huge amount of data, and we've only
analyzed a small part of it so far. Further work is sure to tell us
much more about galaxies and how they evolve. We expect to be surprised,"
Walter said. In addition to the presentations made at the Austin AAS
meeting, THINGS team members also have submitted a series of scientific
papers to the Astronomical Journal.
The THINGS project is a large international collaboration led by
Walter and includes research teams led by Brinks, de Blok,
Michele Thornley of the Bucknell University in the U.S. and
Rob Kennicutt of the Cambridge University in the UK.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
Modified on
Tuesday, 08-Jan-2008 22:01:28 EST
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