ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE

Issued by RAS Press Officers:

Dr Robert Massey
Tel: +44 (0)20 7734 3307 / 4582

Anita Heward
Tel: +44 (0)1483 420904

NATIONAL ASTRONOMY MEETING PRESS ROOM (31 MARCH - 4 APRIL ONLY):
Tel: +44 (0)2890 975262 / 975263 / 975264

NAM 2008
http://nam2008.qub.ac.uk

Royal Astronomical Society
http://www.ras.org.uk

CONTACTS

Will Hartley
Centre for Astronomy and Particle Theory
School of Physics and Astronomy
University of Nottingham
University Park
Nottingham NG7 2RD
United Kingdom
Tel: +44 (0)115 846 8829

Dr Omar Almaini
Centre for Astronomy and Particle Theory
School of Physics and Astronomy
University of Nottingham
University Park
Nottingham NG7 2RD
United Kingdom
Tel: +44 (0)115 846 7901

EMBARGOED UNTIL 0001 BST, 1 April 2008

Ref.: PN 08/13 (NAM 04)

Old galaxies stick together in the young Universe

Using the most sensitive images ever obtained with the United Kingdom
Infra-Red Telescope (UKIRT), astronomers have found convincing evidence that
galaxies which look old early in the history of the Universe reside in
enormous clouds of invisible dark matter and will eventually evolve into the
most massive galaxies that exist in the present day.

University of Nottingham PhD student Will Hartley, who led the study, will
speak at the RAS National Astronomy Meeting in Belfast on Tuesday 1 April.

The distant galaxies identified in the UKIRT images are considered elderly
because they are rich in old, red stars.  However, because the light from
these systems has taken up to 10 billion years to reach Earth, they are seen
as they appeared in the very early Universe, just 4 billion years after the
Big Bang. The presence of such fully evolved galaxies so early in the life
of the cosmos is hard to explain and has been a major puzzle to astronomers
studying how galaxies form and evolve.

Hartley and collaborators used the deep UKIRT images to estimate the mass of
the dark matter surrounding the old galaxies by measuring how strongly the
galaxies cluster together.  All galaxies are thought to form within massive
halos of dark matter which collapse under their own gravity from a smooth
distribution of matter after the Big Bang.

These halos are invisible to normal telescopes but their mass can be
estimated through analysis of galaxy clustering.

Hartley explains: "Luckily, even if we don't know what dark matter is, we
can understand how gravity will affect it and make it clump together. We can
see that the old, red galaxies clump together far more strongly than the
young, blue galaxies, so we know that their invisible dark matter halos must
be more massive.

The halos surrounding the old galaxies in the early Universe are found to be
extremely massive, containing material which is one hundred thousand billion
times the mass of our Sun.  In the nearby Universe, halos of this size are
known to contain giant elliptical galaxies, the largest galaxies known.

"This provides a direct link to the present day Universe," says Hartley,
"and tell us that these distant old galaxies must evolve into the most
massive but more familiar elliptical-shaped galaxies we see around us today. 
Understanding how these enormous elliptical galaxies formed is one of the
biggest open questions in modern astronomy and this is an important step in
comprehending their history."

IMAGES

Image of the elderly galaxies,
   http://www.nottingham.ac.uk/astronomy/UDS/UDS_files/bigger_pBzK3.jpg
(83KB)

Image caption: The white arrows point to a few of the old, massive galaxies
at a distance of 10 billion light years, discovered in the UKIDSS Ultra-Deep
survey. This cut-out image represents just 1/150th of the full survey.
(Credit: UKIDSS UDS survey team)

FURTHER INFORMATION

* The UKIDSS Ultra-Deep Survey
  http://www.nottingham.ac.uk/astronomy/UDS/
* UKIRT
  http://www.jach.hawaii.edu/UKIRT/
* Nottingham Astronomy group
  http://www.nottingham.ac.uk/astronomy/

NOTES FOR EDITORS

The old galaxies were identified from images taken as part of the Ultra-Deep
Survey (UDS), one element of a five-part project, the UKIRT Infrared Deep
Sky Survey (UKIDSS), which commenced in 2005. UKIRT is the world's largest
telescope dedicated solely to infrared astronomy, sited near the summit of
Mauna Kea, Hawaii, at an altitude of 4194 metres (13760 feet) above sea
level.

The RAS National Astronomy Meeting (NAM 2008) is hosted by Queen's
University Belfast. It is principally sponsored by the RAS and the Science
and Technology Facilities Council (STFC). NAM 2008 is being held together
with the UK Solar Physics (UKSP) and Magnetosphere, Ionosphere and
Solar-Terrestrial (MIST) spring meetings.
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