thed
04-14-02, 08:01 AM
From sci.astro again
<img src="http://www.sr.bham.ac.uk/~amr/arp270_rgb.jpg"><img src="http://www.sr.bham.ac.uk/~amr/ARP_270_I_103a-D_a1966.jpg">
Approved:
Royal Astronomical Society Press Notice
Date: 5 April 2002
EMBARGOED UNTIL 7 am BST, THURSDAY 11 APRIL 2002
Ref. PN 02/21 (NAM 15)
Issued by: RAS Press Officers
Peter Bond (Except 8 - 12 April)
Tel: +44 (0)1483-268672
Fax: +44 (0)1483-274047
Mobile phone: +44 (0)7711-213486
E-mail: PeterRBond@cs.com
AND
Dr Jacqueline Mitton (Except 7 - 13 April)
Tel: +44 (0)1223-564914
Fax: +44 (0)1223-572892
Mobile phone: +44 (0)7770-386133
E-mail: jmitton@dial.pipex.com
NAM PRESS ROOM (9 -12 April only):
+44 (0)117 928-4337
+44 (0)117 928-4338
+44 (0)117 954-5913
+44 (0)117 928-7901
UK National Astronomy Meeting Web site:
http://www.star.bris.ac.uk/nam/index.html
CONTACT FOR THIS RELEASE
During the National Astronomy Meeting, Dr. Read can be contacted via
the NAM press office (see above) on Wednesday 10 April and Thursday
11 April.
Normal contact details:
Dr. Andrew Read, Astrophysics & Space Research Group, School of
Physics & Astronomy, University of Birmingham, Watson building:
G16, Birmingham B15 2TT
Tel: +44 (0)121-414-6466 Fax: +44 (0)121-414-3722
E-mail: amr@star.sr.bham.ac.uk
Web: http://www.sr.bham.ac.uk/~amr/
************************************************** ***********
X-RAYS EXAMINE COLLIDING GALAXIES
Galaxies were once thought of as 'island universes' evolving slowly
in complete isolation. This is now known not to be the case. By using
the world's most powerful X-ray observatories, UK astronomers are
discovering that most of these gigantic star systems interact with
each other in a wide variety of ways.
During the UK National Astronomy Meeting in Bristol on Thursday 11
April, Dr. Andrew Read (University of Birmingham) will present new
results from the Chandra and XMM-Newton spacecraft about the nature
of these colliding galaxies. Famous examples of such cosmic
collisions studied by Dr. Read include the 'Antennae', the 'Mice'
and Markarian 266.
"The X-ray properties of merging galaxies are the result of very hot
and energetic phenomena -- massive stars, supernovae and supernova
remnants, collapsed objects (black holes, neutron stars) and hot
diffuse gas," said Read.
"With the recent launch of Chandra and XMM, we can now use the vastly
superior power, sensitivity and resolution of these new X-ray
telescopes to extend our research to study many kinds of merging
galaxy systems."
Several of the bright interacting systems reveal a very diffuse,
extended X-ray emission that seems to arise from very hot (a few
million degrees Celsius) material ejected from the galaxies.
This ejection process seems to begin very soon after the galaxies
first encounter one another and rapidly creates distorted flows of
outflowing gas. Meanwhile, vigorous star formation is seen in the
galactic nuclei and within the merging disks.
Other phenomena, resulting from star formation and expulsion of hot
gas in the early stages of interaction, are seen as the galactic
disks collide. More massive gaseous X-ray ejections (perhaps
involving up to 10 billion solar masses of hot gas) are seen at the
'ultraluminous' peak of the interaction, as the galactic nuclei
coalesce.
In the new Chandra X-ray images, red represents soft (cool) X-ray
emission [0.2-0.9 keV], green intermediate [0.9-2.5 keV] and blue
hard (hot) X-ray emission [2.5-10 keV].
Within Arp 270, a system in the early stages of a merger, the galactic
disks are still very distinct. The X-ray image shows relatively cool
(less than 1 million degrees Celsius) diffuse gaseous emission
associated with the two disks and several point sources of varying
X-ray energy (indicators of varying temperatures) are seen scattered
within the galaxies. Of particular interest are the 'hard' point
sources visible where the disks collide. A new idea that is being
considered is that they may be due to strong star-formation as the
two gaseous disks rotate through each other.
The 'Mice' show bright X-ray features from both galaxy nuclei, and
further emission from within the northern tail. The southern nucleus
appears harder in X-rays than the northern. The northern galaxy,
however, shows what appears to be a small bipolar X-ray outflow --
a great rarity in such a violently evolving, classical merger system.
Markarian 266 consists of two galaxies about to merge. The Chandra
image resolves their nuclei, with the northern nucleus emitting
higher energy X-rays and appearing significantly hotter.
Interestingly, very soft, diffuse gaseous emission is seen to the
north and to the east of the system -- thought to be due to a
stronger, more evolved and more distorted outflow than seen in the
'Mice'.
Observations such as these will enable astronomers to address
important questions, such as when, where and how these ejection
processes occur, and how much energy, gas and metal is injected by
merging galaxies out into the intergalactic medium.
This has profound implications for galactic formation and evolution,
for group/cluster evolution and for the total mass content of the
universe.
NOTES FOR EDITORS:
Collisions and mergers of galaxies are now thought to be one of the
most dominant mechanisms in the evolution of these giant star systems.
Even our own Milky Way galaxy is presently interacting with the nearby
Small and Large Magellanic Clouds, and these will be subsumed by our
own galaxy within the next few hundred million years.
If events during galaxy formation are counted, there are probably
very few galaxies that were not shaped by interactions or even
outright mergers.
The position of a galaxy in Edwin Hubble's famous morphological
sequence of galaxies may in fact depend mainly on the number and
severity of merger events in its past history. Pure disk spiral
systems, formed from relatively isolated protogalactic gas clouds,
appear at one end of the Hubble sequence. The giant ellipticals
(spheroidal galaxies), possibly produced through mergers of similar
spirals, appear at the other end. In between, mergers between
galaxies of differing mass produce galaxies with a wide range of
shapes and sizes.
Arp 270 lies about 90 million light years away.
The 'Mice' is the popular name for two interacting galaxies --
so-called because of their distinctive tails. They are officially
known as NGC 4676 A, B or Arp 242, and lie about 290 million light
years away.
Markarian 266 is a pair of interacting galaxies located some 365
million light years from Earth.
FURTHER INFORMATION AND IMAGES CAN BE FOUND ON THE WEB AT:
http://www.sr.bham.ac.uk/~amr/Chandra.html
RAS Web site:
http://www.ras.org.uk/
UK National Astronomy Meeting Web site:
http://www.star.bris.ac.uk/nam/
<img src="http://www.sr.bham.ac.uk/~amr/arp270_rgb.jpg"><img src="http://www.sr.bham.ac.uk/~amr/ARP_270_I_103a-D_a1966.jpg">
Approved:
Royal Astronomical Society Press Notice
Date: 5 April 2002
EMBARGOED UNTIL 7 am BST, THURSDAY 11 APRIL 2002
Ref. PN 02/21 (NAM 15)
Issued by: RAS Press Officers
Peter Bond (Except 8 - 12 April)
Tel: +44 (0)1483-268672
Fax: +44 (0)1483-274047
Mobile phone: +44 (0)7711-213486
E-mail: PeterRBond@cs.com
AND
Dr Jacqueline Mitton (Except 7 - 13 April)
Tel: +44 (0)1223-564914
Fax: +44 (0)1223-572892
Mobile phone: +44 (0)7770-386133
E-mail: jmitton@dial.pipex.com
NAM PRESS ROOM (9 -12 April only):
+44 (0)117 928-4337
+44 (0)117 928-4338
+44 (0)117 954-5913
+44 (0)117 928-7901
UK National Astronomy Meeting Web site:
http://www.star.bris.ac.uk/nam/index.html
CONTACT FOR THIS RELEASE
During the National Astronomy Meeting, Dr. Read can be contacted via
the NAM press office (see above) on Wednesday 10 April and Thursday
11 April.
Normal contact details:
Dr. Andrew Read, Astrophysics & Space Research Group, School of
Physics & Astronomy, University of Birmingham, Watson building:
G16, Birmingham B15 2TT
Tel: +44 (0)121-414-6466 Fax: +44 (0)121-414-3722
E-mail: amr@star.sr.bham.ac.uk
Web: http://www.sr.bham.ac.uk/~amr/
************************************************** ***********
X-RAYS EXAMINE COLLIDING GALAXIES
Galaxies were once thought of as 'island universes' evolving slowly
in complete isolation. This is now known not to be the case. By using
the world's most powerful X-ray observatories, UK astronomers are
discovering that most of these gigantic star systems interact with
each other in a wide variety of ways.
During the UK National Astronomy Meeting in Bristol on Thursday 11
April, Dr. Andrew Read (University of Birmingham) will present new
results from the Chandra and XMM-Newton spacecraft about the nature
of these colliding galaxies. Famous examples of such cosmic
collisions studied by Dr. Read include the 'Antennae', the 'Mice'
and Markarian 266.
"The X-ray properties of merging galaxies are the result of very hot
and energetic phenomena -- massive stars, supernovae and supernova
remnants, collapsed objects (black holes, neutron stars) and hot
diffuse gas," said Read.
"With the recent launch of Chandra and XMM, we can now use the vastly
superior power, sensitivity and resolution of these new X-ray
telescopes to extend our research to study many kinds of merging
galaxy systems."
Several of the bright interacting systems reveal a very diffuse,
extended X-ray emission that seems to arise from very hot (a few
million degrees Celsius) material ejected from the galaxies.
This ejection process seems to begin very soon after the galaxies
first encounter one another and rapidly creates distorted flows of
outflowing gas. Meanwhile, vigorous star formation is seen in the
galactic nuclei and within the merging disks.
Other phenomena, resulting from star formation and expulsion of hot
gas in the early stages of interaction, are seen as the galactic
disks collide. More massive gaseous X-ray ejections (perhaps
involving up to 10 billion solar masses of hot gas) are seen at the
'ultraluminous' peak of the interaction, as the galactic nuclei
coalesce.
In the new Chandra X-ray images, red represents soft (cool) X-ray
emission [0.2-0.9 keV], green intermediate [0.9-2.5 keV] and blue
hard (hot) X-ray emission [2.5-10 keV].
Within Arp 270, a system in the early stages of a merger, the galactic
disks are still very distinct. The X-ray image shows relatively cool
(less than 1 million degrees Celsius) diffuse gaseous emission
associated with the two disks and several point sources of varying
X-ray energy (indicators of varying temperatures) are seen scattered
within the galaxies. Of particular interest are the 'hard' point
sources visible where the disks collide. A new idea that is being
considered is that they may be due to strong star-formation as the
two gaseous disks rotate through each other.
The 'Mice' show bright X-ray features from both galaxy nuclei, and
further emission from within the northern tail. The southern nucleus
appears harder in X-rays than the northern. The northern galaxy,
however, shows what appears to be a small bipolar X-ray outflow --
a great rarity in such a violently evolving, classical merger system.
Markarian 266 consists of two galaxies about to merge. The Chandra
image resolves their nuclei, with the northern nucleus emitting
higher energy X-rays and appearing significantly hotter.
Interestingly, very soft, diffuse gaseous emission is seen to the
north and to the east of the system -- thought to be due to a
stronger, more evolved and more distorted outflow than seen in the
'Mice'.
Observations such as these will enable astronomers to address
important questions, such as when, where and how these ejection
processes occur, and how much energy, gas and metal is injected by
merging galaxies out into the intergalactic medium.
This has profound implications for galactic formation and evolution,
for group/cluster evolution and for the total mass content of the
universe.
NOTES FOR EDITORS:
Collisions and mergers of galaxies are now thought to be one of the
most dominant mechanisms in the evolution of these giant star systems.
Even our own Milky Way galaxy is presently interacting with the nearby
Small and Large Magellanic Clouds, and these will be subsumed by our
own galaxy within the next few hundred million years.
If events during galaxy formation are counted, there are probably
very few galaxies that were not shaped by interactions or even
outright mergers.
The position of a galaxy in Edwin Hubble's famous morphological
sequence of galaxies may in fact depend mainly on the number and
severity of merger events in its past history. Pure disk spiral
systems, formed from relatively isolated protogalactic gas clouds,
appear at one end of the Hubble sequence. The giant ellipticals
(spheroidal galaxies), possibly produced through mergers of similar
spirals, appear at the other end. In between, mergers between
galaxies of differing mass produce galaxies with a wide range of
shapes and sizes.
Arp 270 lies about 90 million light years away.
The 'Mice' is the popular name for two interacting galaxies --
so-called because of their distinctive tails. They are officially
known as NGC 4676 A, B or Arp 242, and lie about 290 million light
years away.
Markarian 266 is a pair of interacting galaxies located some 365
million light years from Earth.
FURTHER INFORMATION AND IMAGES CAN BE FOUND ON THE WEB AT:
http://www.sr.bham.ac.uk/~amr/Chandra.html
RAS Web site:
http://www.ras.org.uk/
UK National Astronomy Meeting Web site:
http://www.star.bris.ac.uk/nam/