NASA's Chandra Finds Evidence for Quasar Ignition (Forwarded)

Steve Roy
Marshall Space Flight Center, Huntsville, Ala. March 22, 2006
(Phone: 256/544-6535)

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
(Phone: 617/496-7998)

CXC release: 06-02

NASA's Chandra Finds Evidence for Quasar Ignition

Scientists using NASA's Chandra X-ray Observatory have detected an
extensive halo of hot gas around a quiescent spiral galaxy. This discovery
is evidence that galaxies like our Milky Way are still accumulating matter
from the gradual inflow of intergalactic gas.

"What we are likely witnessing here is the ongoing galaxy formation
process," said Kristian Pedersen of the University of Copenhagen, Denmark,
and lead author of a report on the discovery.

Chandra observations show that the hot halo extends more than 60,000 light
years on either side of the disk of the galaxy known as 4C37.43. The
detection of such a large halo alleviates a long-standing problem for the
theory of galaxy formation. Spiral galaxies are thought to form from
enormous clouds of intergalactic gas that collapse to form giant, spinning
disks of stars and gas.

One prediction of this theory is that large spiral galaxies should be
immersed in halos of hot gas left over from the galaxy formation process.
Hot gas has been detected around spiral galaxies in which vigorous star
formation is ejecting matter from the galaxy, but until now hot halos due
to infall of intergalactic matter have not been detected.

"Our observations solve the mystery of the missing hot halos around spiral
galaxies," said Pedersen. "The halos exist, but are so faint that an
extremely sensitive telescope such as Chandra is needed to detect them."
4C37.43 is a massive spiral galaxy about a 100 million light years from
Earth. Its disk of stars and gas is viewed almost edge-on. The galaxy
shows no signs of unusual star formation, or energetic activity from its
nuclear region, making it unlikely that the hot halo is produced by gas
flowing out of the galaxy.

"We targeted 4C37.43 because we thought its distance and orientation would
give us the best chance to detect a hot halo caused by the infall of
intergalactic gas," said Jesper Rasmussen of the University of Birmingham,
United Kingdom and a coauthor of the report. "What we found is in good
agreement with computer simulations in which galaxies are built up
gradually from the merger of smaller clouds of hot gas and dark matter."

The computer simulations were done by Jesper Sommer-Larsen (also a
coauthor of the report) and collaborators at the University of Copenhagen.
The paper describing these results will be published in the April issue of
the journal New Astronomy. Other researchers on this project were Sune
Toft, Yale University; Andrew Benson, University of Oxford, United
Kingdom; and Richard Bower, University of Durham, United Kingdom.

NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra
program for the agency's Science Mission Directorate. The Smithsonian
Astrophysical Observatory controls science and flight operations from the
Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu/photo/2006/4c37/
and
http://www.nasa.gov/centers/marshall/news/chandra/