This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Commonwealth Scientific and Industrial Research Organisation
Australia

Contacts:

Ms Rosie Schmedding
CSIRO Media
PO Box 225
Dickson ACT 2602
Phone: +61 2 6276 6520
Fax: +61 2 6276 6821
Mobile: +61 418 622 653
Email: Rosie.Schmedding{at}csiro.au
   
Ms Helen Sim
Sector Communicator
Australia Telescope National Facility
PO Box 76
Epping NSW 1710
Phone: +61 2 9372 4251
Fax: +61 2 9372 4310
Email: Helen.Sim{at}csiro.au

Media Release: May 06, 2003

Ref 2003/73

'Cosmic dandruff' mystery solved

Recent discoveries made with CSIRO's Parkes telescope appear to have 
settled a 40-year-old controversy about the nature of gas clouds that 
surround our Milky Way Galaxy.

Small 'high-velocity' clouds of hydrogen gas seen outside our Galaxy
are mostly scraps shed by satellite galaxies orbiting the Milky Way,
researchers say -- a kind of cosmic dandruff. They are not the
missing clumps of dark matter predicted by the 'cold dark matter'
theory of galaxy formation.

Dr Mary Putman of the University of Colorado will present this 
conclusion today [Tuesday 6 May] at a meeting about our Galaxy and
its neighbours at the Space Telescope Science Institute in Baltimore
MD. 

Dr Putman and colleagues in Australia used the CSIRO Parkes 64-m
radio telescope in eastern Australia to make the most detailed study
to date of the Magellanic Stream -- a ribbon of hydrogen gas trailing
from the Milky Way's largest satellite galaxies, the Large and Small
Magellanic Clouds. They also studied the high-velocity clouds that
surround the Stream. 

The high-velocity clouds were discovered 40 years ago, but it has
been very difficult to determine exactly how far away and massive
they are. Their nature and origin has been controversial.

Some of the high-velocity clouds are associated with the Magellanic 
Stream, the researchers found.

Others appear to be shed by other satellite galaxies.

"We now have pretty conclusive evidence that the high-velocity clouds 
are not scattered throughout our Local Group of galaxies, but are
within the extended halo of the Milky Way," said Dr Putman.

"Previous studies of other galaxy groups haven't found any
counterparts of the high-velocity clouds," said team member Dr Lister
Staveley-Smith of the CSIRO Australia Telescope National Facility.

"If the clouds are there, they must lie close to the big galaxies
rather than be scattered throughout galaxy groups."

The standard model of galaxy formation predicts that there are
hundreds of small lumps or 'halos' of cold dark matter scattered
throughout the Local Group.

But researchers have failed to find them.

It had been suggested that the high-velocity clouds might be those 
objects. But the new finding means this is highly unlikely.

"If the dark matter halos the models predict are there, they can't be 
associated with large amounts of cold gas," Dr Putman said. "We don't 
find the gas clouds at large distances from galaxies."

"High-velocity clouds are fantastic probes of the properties of the 
Milky Way and its halo," Dr Staveley-Smith said.

"But the question of whether they individually contain much dark
matter remains controversial."

The members of the research team were: Mary E. Putman (Center for 
Astrophysics and Space Astronomy, University of Colorado), Lister 
Staveley-Smith (CSIRO Australia Telescope National Facility), Kenneth
C. Freeman (Research School of Astronomy and Astrophysics, Australian
National University), and Brad K. Gibson and David G. Barnes (both 
Centre for Astrophysics and Supercomputing, Swinburne University of 
Technology). The Parkes telescope is operated by CSIRO Australia 
Telescope National Facility as a national facility.

More information:
Helen Sim
CSIRO Australia Telescope National Facility
+61-2-9372-4251, +61-419-635-905
Email: Helen.Sim{at}csiro.au

Dr Mary Putman
Center for Astrophysics and Space Astronomy
University of Colorado
+1-303-819-2067 (mobile)
During May 5-8: +1-410-338-497 (Space Telescope Science Institute
meeting) and
+1-410-235-5400 ("Doubletree Inn at the Colonnade" hotel)
+1-303-492-6058 (Colorado office)
Email: Mary.Putman{at}colorado.edu

Dr Lister Staveley-Smith
CSIRO Australia Telescope National Facility (Sydney, Australia)
+61-2-9372-4271
Email: Lister.Staveley-Smith{at}csiro.au

Dr Ken Freeman
Research School of Astronomy and Astrophysics
Australian National University
+61-2-6125-0264, +1-410-338-4970
During May 5-8: (Space Telescope Science Institute meeting)
Email: kcf{at}mso.anu.edu.au

Prof. Brad Gibson
Swinburne University of Technology (Melbourne, Australia)
+61-3-9214-8036
Email: bgibson{at}swin.edu.au

Meeting

The Space Telescope Science Institute Spring Symposium
"The Local Group as an Astrophysical Laboratory"
May 5 - 8, 2003
http://sd.stsci.edu/Astrophysical_Laboratory/index.html

Publication details: Mary E. Putman, Lister Staveley-Smith, Kenneth
C. Freeman, Brad K. Gibson and David G. Barnes. "The Magellanic
Stream, High-Velocity Clouds and the Sculptor Group," ApJ, V. 586,
p. 170-194, 2003 March 20

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---