Debris from Galaxy Collisions Can Be Used As a Laboratory to Study Star Formation (Forwarded)

Office of News and Information
University of Massachusetts Amherst

Contact:
Mederic Boquien, 413/275-7503

June 3, 2008

No. 321-08

Debris from Galaxy Collisions Can Be Used As a Laboratory to Study Star
Formation, Says UMass Amherst Researcher

AMHERST, Mass. -- An international team of researchers led by Mederic
Boquien of the University of Massachusetts Amherst has shown that debris
formed when two galaxies collide makes a simpler, more accessible laboratory
for studying the process of star formation. The team presented their results
at a press conference Monday, June 2 at the American Astronomical Society
meeting in St. Louis, Missouri.

"Surprisingly, we found that star formation is essentially the same in
galaxies and in the debris which occurs between galaxies, in spite of
tremendous differences in the environment," says Boquien, a post-doctoral
researcher in the astronomy department. "This is a very exciting result,
meaning that we can use these regions, which are located outside a
pre-existing stellar disk and are much simpler than star forming regions in
galaxies, to study the creation of stars."

Additional members of the team include Pierre-Alain Duc of the National
Center for Scientific Research in France, Frederic Bournaud of the French
Atomic Energy Commission, Jonathan Braine of the Bordeaux Observatory,
Vassilis Charmandaris of the University of Crete, Greece and Ute Lisenfeld
at the University of Granada, Spain.

Collision debris is the remains of a collision between two or more galaxies,
in which the interplay of gravity can create long expanding "tidal tails."
This debris, which is ejected into the intergalactic medium located between
galaxies, is composed mainly of gas and dust stripped from their parent
galaxies. They can be as heavy as several billion suns, and serve as a
reservoir that feeds star formation. The most massive of these star forming
regions, called tidal dwarf galaxies, can be bound by their own gravity and
rotate.

Barely studied since their discovery in the 1950s, these areas have sparked
increasing interest from astronomers, and were recently used to test the
nature of dark matter. What was not known was whether star formation was the
same in collision debris as it was in galaxies, a key factor in determining
their usefulness in the study of star formation.

To answer this question, Boquien and his team observed a carefully selected
sample of six interacting galaxy systems located a distance of 55 to 375
million light years from Earth. The study focused on extreme systems in
which a large fraction (up to 85%) of star formation takes place in
collision debris, rather than in the main body of the parent galaxies, a
situation that is representative of the distant, young Universe.

By simultaneously analyzing multiple wavelengths of emissions, including
infrared radiation from the dust heated by young stars picked up by the
Spitzer space observatory, the team was able to trace star formation and
determine that the process was occurring in essentially the same way in the
intergalactic medium and inside galaxies. Ultraviolet energy detected by the
Galaxy Evolution Explorer and images of ionized hydrogen atoms and optical
and infrared light from eight ground-based telescopes were also used.

"The best regions to study stellar evolution would be those completely
devoid of old stars, and we were able to find some regions which satisfy
this criteria," says Boquien, who adds that these regions are generally
quite isolated, unlike star forming regions in galaxies which can be
surrounded by many bright astronomical objects. "As star formation
apparently occurs in a similar way in galaxies, results we obtain studying
intergalactic star forming regions can be confidently extended to galaxies."