Andrew Yee
April 6th 06, 04:26 PM
ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
Issued by RAS Communications Officers:
Anita Heward
Tel: +44 (0)1483-420904
AND
Peter Bond
Tel: +44 (0)1483-268672 Fax: +44 (0)1483-274047
National Astronomy Meeting Press Room (4 - 7 April only):
Tel: +44 (0)116-229-7474 or 229-7475 or 252-3312 or 252-3531
Fax: +44 (0)116-252-3531
RAS Web site:
http://www.ras.org.uk/
RAS National Astronomy Meeting web site:
http://www.nam2006.le.ac.uk/index.shtml
CONTACT DETAILS ARE LISTED AT THE END OF THIS RELEASE.
EMBARGOED FOR 00:01 BST, WEDNESDAY, 5 APRIL 2006
Ref.: PN 06/19 (NAM12)
Gemini/HST survey shows building-blocks in evolution of massive galaxy
clusters
A study of the Universe's most massive galaxy clusters has shown that
mergers play a vital role in their evolution.
Astronomers at Oxford University and the Gemini Observatory used a
combination of data from the twin Gemini Telescopes, located in Hawaii and
Chile, and the Hubble Space Telescope (HST) to study populations of stars
in the Universe's most massive galaxy clusters over a range of epochs --
the earliest being half the age of the Universe. The HST images were used
to map the light distribution of the galaxies in the cluster. Data from
the Gemini Multi-Object Spectrograph allowed the team to analyse the light
from galaxies to determine their masses, ages and chemical compositions.
"We still don't have a clear picture of how galaxies develop over the
history of the Universe. The strength of this study is that we are able to
look at galaxy clusters over a range of epochs," said Dr Jordi Barr of
Oxford University, who is presenting some of the first results of the
Gemini/HST Galaxy Cluster Project at the RAS National Astronomy Meeting on
5th April.
Galaxy clusters contain the most massive galaxies in the Universe. Until
recently, astronomers believed that all galaxies in the centres of
clusters formed rapidly and then aged without any further changes to their
structure in a process known as "Passive Evolution". Results from the
Gemini/HST Galaxy Cluster Project now show that this cannot be the case.
Dr Barr explained, "When we're looking at the most distant galaxy
clusters, we are looking back in time to clusters that are in early stages
of their formation. The young galaxies in distant clusters appear to be
very different from those in the mature clusters that we see in the local
Universe. We found the earliest galaxy clusters have a huge variation in
the abundances of elements such as oxygen and magnesium, whereas the
chemistry of galaxies in the sample of closer clusters appears to be much
more homogenous. This difference in chemistry proves that the clusters
must actively change over time. If the galaxies in the old clusters have
acquired a complete 'set' of elements, it's most likely that they have
formed from the mergers of several young galaxies."
The group found that the star-formation in galaxies is dependent on mass
and that in lower mass galaxies star-formation continues for longer. The
most massive galaxies in clusters appear to have formed all their stars by
the time the universe is just over a billion years old, whereas the lower
mass galaxies finish forming their stars some 4 billion years later.
"We see the effects of star-formation in low mass galaxies but are unsure
about why it's happening. It's possible that star-formation can be shut
down very rapidly in dense environments and that the lower mass galaxies
are recent arrivals that are forming stars over a longer period outside
the cluster, then falling in. But we are still speculating ..." said Dr
Barr
The group's observations of merging galaxy clusters showed that a large
proportion of the galaxies in those clusters have undergone recent bursts
of star formation. This indicates that star formation may be triggered if
galaxies are thrown, during the course of a merger, into contact with the
gaseous medium pervading the cluster.
Future observations are planned at X-ray wavelengths to study the
interactions between galaxies and the distribution and temperature of the
surrounding gas.
IMAGES
[http://hubblesite.org/gallery/album/entire_collection/pr2003001a/]
Hubble Space Telescope image of Abell 1689, one of the galaxy clusters
used in sample for the study. © NASA, N. Benitez (JHU), T. Broadhurst
(Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M.
Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory),
the ACS Science Team and ESA
FURTHER INFORMATION
Royal Astronomical Society's National Astronomy Meeting
The 2006 RAS National Astronomy Meeting is hosted by the University of
Leicester. It is sponsored by the Royal Astronomical Society, the UK
Particle Physics and Astronomy Research Council (PPARC), the University of
Leicester and the National Space Centre, Leicester.
CONTACTS
Dr Jordi Barr
Denys Wilkinson Building
Keble Road
Oxford OX1 3RH, UK
Tel: +44 (0)1865 273 299
Fax: +44 (0)1865 273 390
Web: http://www-astro.physics.ox.ac.uk/~jmb/
Issued by RAS Communications Officers:
Anita Heward
Tel: +44 (0)1483-420904
AND
Peter Bond
Tel: +44 (0)1483-268672 Fax: +44 (0)1483-274047
National Astronomy Meeting Press Room (4 - 7 April only):
Tel: +44 (0)116-229-7474 or 229-7475 or 252-3312 or 252-3531
Fax: +44 (0)116-252-3531
RAS Web site:
http://www.ras.org.uk/
RAS National Astronomy Meeting web site:
http://www.nam2006.le.ac.uk/index.shtml
CONTACT DETAILS ARE LISTED AT THE END OF THIS RELEASE.
EMBARGOED FOR 00:01 BST, WEDNESDAY, 5 APRIL 2006
Ref.: PN 06/19 (NAM12)
Gemini/HST survey shows building-blocks in evolution of massive galaxy
clusters
A study of the Universe's most massive galaxy clusters has shown that
mergers play a vital role in their evolution.
Astronomers at Oxford University and the Gemini Observatory used a
combination of data from the twin Gemini Telescopes, located in Hawaii and
Chile, and the Hubble Space Telescope (HST) to study populations of stars
in the Universe's most massive galaxy clusters over a range of epochs --
the earliest being half the age of the Universe. The HST images were used
to map the light distribution of the galaxies in the cluster. Data from
the Gemini Multi-Object Spectrograph allowed the team to analyse the light
from galaxies to determine their masses, ages and chemical compositions.
"We still don't have a clear picture of how galaxies develop over the
history of the Universe. The strength of this study is that we are able to
look at galaxy clusters over a range of epochs," said Dr Jordi Barr of
Oxford University, who is presenting some of the first results of the
Gemini/HST Galaxy Cluster Project at the RAS National Astronomy Meeting on
5th April.
Galaxy clusters contain the most massive galaxies in the Universe. Until
recently, astronomers believed that all galaxies in the centres of
clusters formed rapidly and then aged without any further changes to their
structure in a process known as "Passive Evolution". Results from the
Gemini/HST Galaxy Cluster Project now show that this cannot be the case.
Dr Barr explained, "When we're looking at the most distant galaxy
clusters, we are looking back in time to clusters that are in early stages
of their formation. The young galaxies in distant clusters appear to be
very different from those in the mature clusters that we see in the local
Universe. We found the earliest galaxy clusters have a huge variation in
the abundances of elements such as oxygen and magnesium, whereas the
chemistry of galaxies in the sample of closer clusters appears to be much
more homogenous. This difference in chemistry proves that the clusters
must actively change over time. If the galaxies in the old clusters have
acquired a complete 'set' of elements, it's most likely that they have
formed from the mergers of several young galaxies."
The group found that the star-formation in galaxies is dependent on mass
and that in lower mass galaxies star-formation continues for longer. The
most massive galaxies in clusters appear to have formed all their stars by
the time the universe is just over a billion years old, whereas the lower
mass galaxies finish forming their stars some 4 billion years later.
"We see the effects of star-formation in low mass galaxies but are unsure
about why it's happening. It's possible that star-formation can be shut
down very rapidly in dense environments and that the lower mass galaxies
are recent arrivals that are forming stars over a longer period outside
the cluster, then falling in. But we are still speculating ..." said Dr
Barr
The group's observations of merging galaxy clusters showed that a large
proportion of the galaxies in those clusters have undergone recent bursts
of star formation. This indicates that star formation may be triggered if
galaxies are thrown, during the course of a merger, into contact with the
gaseous medium pervading the cluster.
Future observations are planned at X-ray wavelengths to study the
interactions between galaxies and the distribution and temperature of the
surrounding gas.
IMAGES
[http://hubblesite.org/gallery/album/entire_collection/pr2003001a/]
Hubble Space Telescope image of Abell 1689, one of the galaxy clusters
used in sample for the study. © NASA, N. Benitez (JHU), T. Broadhurst
(Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M.
Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory),
the ACS Science Team and ESA
FURTHER INFORMATION
Royal Astronomical Society's National Astronomy Meeting
The 2006 RAS National Astronomy Meeting is hosted by the University of
Leicester. It is sponsored by the Royal Astronomical Society, the UK
Particle Physics and Astronomy Research Council (PPARC), the University of
Leicester and the National Space Centre, Leicester.
CONTACTS
Dr Jordi Barr
Denys Wilkinson Building
Keble Road
Oxford OX1 3RH, UK
Tel: +44 (0)1865 273 299
Fax: +44 (0)1865 273 390
Web: http://www-astro.physics.ox.ac.uk/~jmb/