An international team of astronomers have used a unique instrument on the
8-m Gemini South Telescope to determine the ages of stars across the central
region of the barred spiral galaxy, M83. Preliminary results provide the
first hints of a domino model of star formation where star formation occurs
in a time sequence, driven by the movements of gas and stars in the central
bar.

The new instrument, called CIRPASS, simultaneously produces 500 spectra,
taken from across the whole region of interest, which act as a series of
“fingerprints”. Encoded in these “fingerprints” is not only all the
information the team required to determine when individual groups of stars
formed, but also information on their movements and chemical properties. Dr.
Johan Knapen, project co-investigator said, “The unique combination of a
state-of-the-art instrument like CIRPASS with one of the most powerful
telescopes available is now providing us with truly sensational
observations.”

M83 is a “grand-design” spiral galaxy undergoing an intense burst of star
formation in its central bar region. Large-scale images of the visible light
from the galaxy, taken with ground based telescopes, show a pronounced bar
across the middle of the galaxy, seen as a diagonal white structure.
Astronomers believe that it is the influence of this bar that leads a
concentration of gas in the central regions of the galaxy from which stars
are born. “The central region of M83 is enshrouded in dust but, by using
CIRPASS, which operates in the infra-red not the visible, we are able to see
through this dust and investigate the hidden physical processes at work in
the galaxy,” said Dr Ian Parry, leader of the CIRPASS instrumentation team.

Two competing theories strive to explain the burst of star formation in the
centre of the galaxy, M83. One theory suggests that stars form randomly
across the whole nuclear region. A second model, favoured by the
observational team, proposes that star-formation is triggered by the bar
structure. In this model, the rotation of gas and stars in the bar causes
stars to be formed sequentially, in a domino manner.

Using a technique first demonstrated by Dr. Stuart Ryder and colleagues, the
team searched for a hydrogen emission feature, the Paschen-beta line, within
the galaxy’s “fingerprints”. The measurement of this feature indicates the
presence of hot young stars. By comparing the strengths of the Paschen-beta
emission with the amount of absorption from carbon-monoxide (arising in the
cool atmospheres of old giant stars) the team are able determine the age of
the stars in each region of the galaxy. “A detailed analysis of the data is
underway but initial results hint at a complex sequence of star formation,”
said Dr Robert Sharp, instrument support scientist with CIRPASS.

Preliminary analysis of other emission features (due to Paschen-beta and
ionized iron) revealed a potentially intriguing result. “Ionized iron
enables us to trace past supernova explosions. The observations indicate
that energy from exploding stars (supernovae) may be being passed into
regions of undisturbed gas causing further massive star formation,” said Dr.
Stuart Ryder, principle investigator.

While some members of the instrument team are presenting their work at an
exhibition at the Royal Society Science in London on 1st, 2nd and 3rd July,
CIRPASS is back on the Gemini South Telescope in Chile, performing the next
set of observations.

Images and more information are available at:

http://www.ast.cam.ac.uk/~ljw/Press/cirpass_final.html

Contacts:

Robert Sharp, email: rgs@ast.cam.ac.uk, Tel: +44 (0)1223 337148
(In Chile, until mid-July, contactable by e-mail)

Ian Parry, email: irp@ast.cam.ac.uk, Tel: +44 (0)1223 337092

Stuart Ryder, email: sdr@aaoepp.aao.gov.au

Johan Knapen, email: knapen@star.herts.ac.uk

Lisa M. Mazzuca, email : mazzuca@stargate.gsfc.nasa.gov

For general contact information and assistance
Lisa Wright, email:ljw@ast.cam.ac.uk, Tel: +44 (0)1223 337527