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.
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
"The range of light wavelengths to which SIRTF is sensitive allows us to
One important part of the SINGS project is that it includes a good deal of
"By the time our project is completed, this will be the most thoroughly
A strictly observational goal is to build the tools astronomers need to more
SINGS will also shed light on the nature of starburst galaxies. These nearby
Members of the SINGS team include:
complicated problem. It
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."
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. We
able to see a wide range of environments in galaxies a thousand times bigger
than the Milky Way."
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.
observed set of galaxies ever put together," Kennicutt said.
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 Telescope
NICMOS, a project headed by UA astronomy Professor Roger Thompson, and that
will again be observed with SIRTF.
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.
