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RAS PN 08/13 (NAM 04): Old galaxies stick together in the young Universe

Last Updated on Tuesday, 06 April 2010 18:31
Published on Tuesday, 01 April 2008 00:01
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.

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Date:  28 March 2008
Ref.: PN 08/13 (NAM 04)

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RAS PN 08/13 (NAM 04): (EMBARGOED) 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

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


Nottingham Astronomy group
http://www.nottingham.ac.uk/astronomy/

RAS National Astronomy Meeting

RAS home page

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.

CONTACTS

Will Hartley
Centre for Astronomy and Particle Theory
School of Physics and Astronomy
University of Nottingham
University Park
Nottingham NG7 2RD
United Kingdom
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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
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Tel: +44 (0)115 846 7901