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ASTRONOMERS WILL USE SIRTF TO STUDY STAR FORMATION IN NEARBY GALAXIES
From Lori Stiles, UA News Services, 520-621-1877
April 10, 2003


Our Milky Way galaxy will produce about one new star this year. But
this year other nearby galaxies will pump out hundreds of new stars.
Still other nearby galaxies gave birth to their last star about 10
billion years ago. 

Astronomers will use all three Space Infrared Telescope Facility
(SIRTF) science instruments in nearly all modes to discover why some
of our galactic neighbors are prolific or now barren in a SIRTF
Legacy Science Program called "SINGS." SIRTF is planned for launch
Friday, April 18. 

"Our program begins in earnest about four months after launch," said
University of Arizona astronomy Professor Robert C. Kennicutt Jr. He
leads a team of 22 scientists based at the UA Steward Observatory,
the Space Telescope Science Institute in Baltimore, Md., Caltech's
SIRTF Science Center and six other institutions in the "SIRTF Nearby
Galaxy Survey," or SINGS.

------------------------
Contact Information
Robert C. Kennicutt
520-621-4032
robk{at}as.arizona.edu
-----------------------

Five other teams, including one headed by UA astronomer Michael R.
Meyer, also were chosen for the SIRTF Legacy Science Program. The six
projects comprise more than 3,000 hours of observations, or about
half the time available during SIRTF's first year of operation.

The fourth and last of NASA's Great Observatories, SIRTF will view
the universe at very long wavelengths, the far infrared, and see
objects that are too cool, too dust-enshrouded or too far away to
otherwise be seen. The three previous Great Observatories are the
Hubble Space Telescope, Compton Gamma Ray, and Chandra X-ray
Observatories. SIRTF is managed for NASA by the Jet Propulsion
Laboratory, Pasadena, Calif. 

The SIRTF telescope is designed to operate at a temperature of only a
few degrees above absolute zero, and it carries three science
instruments. One of these is a highly sensitive camera called MIPS
that uses the first true imaging arrays at far-infared wavelengths
and will see the coolest objects in space. It was built by a team
headed by the UA astronomy Professor George H. Rieke.

The SINGS team will survey 75 galaxies up to 100 million light years
away in the Virgo supercluster of galaxies, the supercluster that
contains the Milky Way, to learn more about how stars form from dust
and gas. The 75 galaxies include about every nearby kind imaginable.
They differ in how much infrared light they emit relative to visible
light, by morphology or type, and by as much as 100,000 times in
mass.

"We chose galaxies to represent the full range of galaxies in the
local population," Kennicutt said. "Some are spiral, some elliptical.
Some aren't forming many stars at all, others are forming stars 100
times faster than the Milky Way. Some are very dusty and emit most of
their light in the infrared, and some have no dust at all. Some are
interacting galaxies, some exist by themselves.

"We picked as representative a sample of nearby galaxies as possible
because part of the goal of all the Legacy Programs is not only to
focus on a specific science program, but also to build a library of
data that other scientists can build on as well," Kennicutt said.

Why nearby galaxies have such different star formation rates is a
complicated problem. Itšs not simply that star formation is regulated
by the amount of gas present in the galaxy. "When a lot of stars form
in one place, they tend to disperse the gas and quench star
formation," Kennicutt noted. "So the way in which the interstellar
medium and young stars interact is more like a complex ecosystem."

"The range of light wavelengths to which SIRTF is sensitive allows us
to trace every phase of gas that surrounds a star-forming region. It
can probe the cold molecular gas from which stars form, the ionized
gas lit up by hot stars, and the warm gas in between. Up to now,"
Kennicutt said, "those processes have only been studied up close in
our own Milky Way. Wešll be able to see a wide range of environments
in galaxies a thousand times bigger than the Milky Way."

One important part of the SINGS project is that it includes a good
deal of observing time on ground-based telescopes, he added. The
SINGS team won 50 nights of observing time at Kitt Peak and Cerro
Tololo telescopes and almost 100 nights on UA Steward Observatory
telescopes. In addition, other astronomers have been observing the
galaxies on the Very Large Array in Socorro, N.M., and other radio
telescopes in Europe and Australia. Collaborating Caltech astronomers
intend to observe the sample in the ultraviolet with another
satellite, GALEX, that is scheduled for launch later this spring.

"By the time our project is completed, this will be the most
thoroughly observed set of galaxies ever put together," Kennicutt
said.

A strictly observational goal is to build the tools astronomers need
to more accurately measure how much star formation actually does take
place in nearby galaxies. Astronomers can then apply those tools not
only to the 75 galaxies in the SINGS sample, but to high redshift
galaxies that were observed in the 1990s with the Hubble Space
Telescopešs infrared instrument NICMOS, a project headed by UA
astronomy Professor Roger Thompson, and that will again be observed
with SIRTF. 

SINGS will also shed light on the nature of starburst galaxies. These
nearby objects are extremely active in forming stars and are believed
to be analogs of the type of galaxy that was common 15 billion or 10
billion years ago, Kennicutt said. The Hubble Space Telescope
revealed very distant young galaxies in the famous Hubble Deep Field
images, but the infant galaxies are seen as single blobs of light.
Much of what SINGS discovers about nearby baby-boom galaxies can be
used to understand the distant infant galaxies, he added.

Members of the SINGS team include:

*    UA Steward Observatory ­ Kennicutt (principal investigator),
George Rieke, Marcia Rieke, George Bendo, Chad Englebracht, Karl
Gordon, Aigen Li, J.D. Smith
*    Bucknell University ­ Michele Thornley
*    Caltech ­ Lee Armus, George Helou, Thomas Jarrett, Helene Roussel
*    Harvard/Smithsonian Center for Astrophysics ­ Lisa Kewley
*    NASA Ames Research Center ­ David Hollenbach
*    National Radio Astronomy Observatory ­ Fabian Walter
*    Princeton University ­ Bruce Draine
*    Space Telescope Science Institute ­ Daniela Calzetti, Claus
Leitherer, Michael Regan, Sangeeta Malhotra
*    University of Wyoming ­ Daniel Dale

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