Gemini Uncovers 'Lost City' of Stars (Forwarded)

Gemini Observatory
Hilo, Hawaii

Media Contacts:

Peter Michaud
Gemini Observatory, Hilo HI
(808) 974-2510 (Office)

Helen Sim
Anglo-Australian Observatory
+61-2-9372-4251 (Office)

Science Contacts:

Joss Bland-Hawthorn
Anglo-Australian Observatory
Sydney, Australia
+61-2-9372-4851(Office)

Bruce Draine
Princeton University
(609) 258-3810 (Office)

Ken Freeman
Australian National University
Canberra, Australia
+61-2-6125-0264 (Office)

Gemini Uncovers 'Lost City' of Stars

For Immediate Release: August 10, 2005

Like archaeologists unearthing a 'lost city,' astronomers using the
8-meter Gemini South telescope have revealed that the galaxy NGC 300 has
a large, faint extended disk made of ancient stars, enlarging the known
diameter of the galaxy by a factor of two or more.

The finding also implies that our own Milky Way Galaxy could be much
larger than current textbooks say. Scientists will also need to explain
the mystery of how galaxies like NGC 300 can form with stars so far from
their centers.

The research, by an Australian and American team of scientists was just
published in the August 10, 2005 issue of the Astrophysical Journal.

The team used the Gemini Multi-Object Spectrograph on the Gemini South
telescope in Chile, and were able to clearly resolve extremely faint
stars in the disk up to 47,000 light-years from the galaxy's center --
double the previously known radius of the disk. To detect these stars,
images were obtained that went more than ten times 'deeper' than any
previous images of this galaxy (Figure 1).

"A few billion years ago the outskirts of NGC 300 were brightly lit
suburbs that would have shown up as clearly as its inner metropolis,"
said the paper's lead author, Professor Joss Bland-Hawthorn of the
Anglo-Australian Observatory in Sydney, Australia. "But the suburbs have
dimmed with time, and are now inhabited only by faint, old stars --
stars that need large telescopes such as Gemini South to detect them."

The finding has profound implications for our own galaxy since most
current estimates put the size of our Milky Way at about 100,000
light-years or about the size now estimated for NGC 300. "However, the
galaxy is much more massive and brighter than NGC 300 so on this basis,
our galaxy is also probably much larger than we previously thought --
perhaps as much as 200,000 light-years across," said Bland-Hawthorn.

The Galaxy That Keeps On Keeping On!

Adding to these compelling findings is the fact that the team found no
evidence for truncating, or an abrupt 'cutting-off' of the star
population as seen in many galaxies further from the central regions.

Team member Professor Bruce Draine of Princeton University explains:
"It's hard to understand how such an extensive stellar disk that falls
off so smoothly in density could have formed -- this is really a huge
surprise to us. Because it takes an incredibly long time to evenly
disperse stars from a galaxy's central disk to these extreme distances,
it seems more likely that we are seeing the results of star formation
that took place long ago, perhaps as much as ten billion years ago."

"We now realize that there are distinctly different types of galaxy
disks," said team member Professor Ken Freeman of the Research School of
Astronomy and Astrophysics at the Australian National University.
"Probably most galaxies are truncated -- the density of stars in the
disk drops off sharply. But NGC 300 just seems to go on forever. The
density of stars in the disk falls off very smoothly and gradually."

The observers traced NGC 300's disk out to the point where the surface
density of stars was equivalent to a one-thousandth of a sun per square
light-year. "This is the most extended and diffuse population of stars
ever seen," said Bland-Hawthorn.

NGC 300 is a spiral member of the Sculptor group of galaxies, the
closest extragalactic cluster to us, and is about 6.1 million
light-years away. Most of its stars lie in a fairly flat disk making it
appear to be a very normal spiral galaxy like our Milky Way. NGC 300 is
the first galaxy outside of our Local Group to be studied to this depth.
There have only been two others studied to such faint levels, the
Andromeda galaxy and its neighbor M33, both in our Local Group (see
adjacent background information box).

The researchers have been granted more time on Gemini South to determine
exactly what kind of stars they are seeing in the outskirts of NGC 300,
and to make similar studies of other galaxies.

"We still have a lot to learn about how galaxies like ours formed," said
Bland-Hawthorn. "Our next Gemini observations, that we have planned for
later this year, should provide even more important clues and hopefully
even more surprises!"

Images and other resources available at

http://www.gemini.edu/index.php?opti...1&limitstart=1


SIDEBAR
Extended Galactic Disks: What We Know, What We Don't Know...

How did the stars get into the distant reaches of galaxies like NCG 300?
Were they formed in place or are they the result of captures or external
interactions?

It is difficult to explain how hydrogen gas could have come into the
outer regions of NGC 300 -- either by accreting onto the galaxy as gas
per se, or dumped in by mergers with other small galaxies -- and still
left the disk density so smooth.

Mixing processes could have scattered stars out from the inner parts of
the disk. "It's hard to see how that could produce such an extensive
stellar disk that falls off so smoothly in density," says Ken Freeman of
the Research School of Astronomy and Astrophysics at the Australian
National University.

The reason why these outer regions are so faint compared the bright disk
is due to the relative scarcity of hydrogen in the out-lying regions
from which to build new generations of stars (as happens frequently in
the inner disk).

In May 2005 another research team using the W.M. Keck Observatory on
Mauna Kea announced that the Andromeda galaxy was also twice as large as
previously thought. Much like NGC 300, the disk just keeps on going.
However, this is not the case for the other Local Group galaxy, M33,
which shows clear evidence of truncation in its outer regions.

Many independent teams are working on this problem using the new
generation of 8- to 10- meter-class telescopes like Gemini.

To be continued ...

"Andrew Yee" schreef in bericht
...
Gemini Observatory
Hilo, Hawaii

Media Contacts:

Peter Michaud
Gemini Observatory, Hilo HI
(808) 974-2510 (Office)

Helen Sim
Anglo-Australian Observatory
+61-2-9372-4251 (Office)

Science Contacts:

Joss Bland-Hawthorn
Anglo-Australian Observatory
Sydney, Australia
+61-2-9372-4851(Office)

Bruce Draine
Princeton University
(609) 258-3810 (Office)

Ken Freeman
Australian National University
Canberra, Australia
+61-2-6125-0264 (Office)

Gemini Uncovers 'Lost City' of Stars

For Immediate Release: August 10, 2005

Like archaeologists unearthing a 'lost city,' astronomers using the
8-meter Gemini South telescope have revealed that the galaxy NGC 300 has
a large, faint extended disk made of ancient stars, enlarging the known
diameter of the galaxy by a factor of two or more.

The finding also implies that our own Milky Way Galaxy could be much
larger than current textbooks say. Scientists will also need to explain
the mystery of how galaxies like NGC 300 can form with stars so far from
their centers.

The research, by an Australian and American team of scientists was just
published in the August 10, 2005 issue of the Astrophysical Journal.

The team used the Gemini Multi-Object Spectrograph on the Gemini South
telescope in Chile, and were able to clearly resolve extremely faint
stars in the disk up to 47,000 light-years from the galaxy's center --
double the previously known radius of the disk. To detect these stars,
images were obtained that went more than ten times 'deeper' than any
previous images of this galaxy (Figure 1).

"A few billion years ago the outskirts of NGC 300 were brightly lit
suburbs that would have shown up as clearly as its inner metropolis,"
said the paper's lead author, Professor Joss Bland-Hawthorn of the
Anglo-Australian Observatory in Sydney, Australia. "But the suburbs have
dimmed with time, and are now inhabited only by faint, old stars --
stars that need large telescopes such as Gemini South to detect them."

The finding has profound implications for our own galaxy since most
current estimates put the size of our Milky Way at about 100,000
light-years or about the size now estimated for NGC 300. "However, the
galaxy is much more massive and brighter than NGC 300 so on this basis,
our galaxy is also probably much larger than we previously thought --
perhaps as much as 200,000 light-years across," said Bland-Hawthorn.

This is a very interesting finding because the subject is here visible
matter
and what this finding implies is that our galaxy contains more visible
matter
in the outer disk than original thought.
And this in turn has consequences for the amount
of darkmatter in order to explain the (flat) rotation curve of our galaxy:
If there is more visible matter than you need less dark matter.
(And maybe almost none ?)
You cannot have them both.

For more detail goto:
http://users.pandora.be/nicvroom
Goto subject 9: dark matter.
Or goto program 2
http://users.pandora.be/nicvroom/program2.htm
Or to the program written in Excell
http://users.pandora.be/nicvroom/circ11.xls.htm

Nicolaas Vroom