INTERNATIONAL ASTRONOMICAL UNION
XXIVth GENERAL ASSEMBLY, MANCHESTER, UK
7 – 18 August 2000
Media release
From Jacqueline Mitton (Meeting Press Officer)
jmitton@dial.pipex.com
phone: +44 (0)1223 564914
Phone contact 7 – 16 August [Meeting Press Room]
+44 (0)161 275 7832
+44 (0)161 275 9458
+44 (0)161 275 9499
Mobile phone 07770 386133
CONTACTS FOR THIS RELEASE:
Dr Tom Shanks
Tom.Shanks @durham.ac.uk
Phone: +44 (0) 191 374 2171
Dr Nigel Metcalfe
Nigel Metcalfe@durham.ac.uk
Phone: +44 (0) 191 374 3806
Department of Physics, University of Durham
South Road, Durham DH1 3LE, UK
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Summary: So many bright galaxies are now being detected at very high redshift (z > 4), galaxies must be even older and have formed even earlier than previously thought.
Astronomers at Durham University (UK) have found new evidence that large numbers of galaxies were in existence at even earlier times than previously thought. They have identified many galaxies with redshifts between 4 and 6. This means they were already in existence about 10 billion years ago, when the universe was six times smaller than it is now. With this discovery, researchers may have to rethink their ideas about how galaxies formed. The work will be presented on Thursday 17th August by Dr Tom Shanks at a symposium during the International Astronomical Union General Assembly in Manchester (UK).
Because of the finite speed of light, pictures of very remote galaxies (identifiable because their redshifts have high values) record them as they appeared many billions of years ago, or even in the process of formation. Observations of this kind directly test cosmological theories about how and when galaxies formed. The most popular theories so far have said that galaxies formed relatively recently and predict that hardly any galaxies should be seen with high redshifts.
Now, new red and infra-red pictures have been taken of small areas of the sky already targetted by the deepest ultraviolet and blue surveys. The new images extend the search for galaxies to higher redshifts than every before. Surprisingly, the new results show such large numbers of galaxies that there seems to be almost as many bright galaxies with redshifts of 5 as there are at low redshifts nearby! This makes the epoch of galaxy formation earlier in the history of the universe than astronomers previously thought.
Beyond The Final Frontier!
The ground-based pictures come from the UK/Dutch 4.2-metre William Herschel Telescope in the Canary Islands and from the 3.5-metre Calar Alto Telescope in Spain. Tens of hours of exposure time went into a picture taken in red light at the Herschel Telescope with another similarly long exposure made in infrared light at Calar Alto. These pictures have been compared to new pictures in infrared light taken with the Hubble Space Telescope in its Hubble Deep Field North and to new optical and infrared pictures in the Hubble Deep Field South. The Space Telescope exposure was a total of 120 hours in a single tiny patch of sky, observing in ultraviolet, blue and red light. The Space Telescope pictures reach deeper (i.e. can see fainter objects) than the ground-based pictures but they cover a smaller area of sky. However, the basic result is that the counts of high redshift galaxies from both the ground- and space-based experiments agree well, in the range where they can be compared and so both these experiments appear to be giving consistent results.
In 1996, the ultraviolet and blue pictures in the Herschel and Hubble Deep Fields revealed so many faint blue galaxies at a redshift of 2 that they already challenged the claims of the most popular cosmological theory, which suggested that galaxies formed around a redshift of 1, when the universe was half as big as it is now. Since then, observations by Charles Steidel and collaborators at the 10-metre Keck telescope confirmed the Durham group’s results by finding many galaxies at redshifts of 3 and 4. Now, applying similar techniques as before but to the new red and infra-red pictures, Dr Shanks and colleagues find large numbers of galaxies at the even higher redshifts of 5 to 6. There are as many galaxies at these high redshifts as are found locally.
Dr Shanks says, "Four years ago, we described the galaxies we found at with redshifts of 2 as being at ‘The Final Frontier’ because we thought that just beyond them we might be looking back to a time before galaxies formed. Now that large numbers of galaxies at even higher redshifts have been found, we feel entitled to describe them as being Beyond the Final Frontier!".
BACKGROUND NOTES
Deep Pictures as Time Machines.
Light travels at a speed of 300,000 kilometres per second. Although this speed is high it is finite and this means that light takes about 8 minutes to reach us from the Sun. The huge size of our Milky Way Galaxy means that light takes about 25,000 years to reach us from the Centre of our Galaxy. But the light from the faint galaxies seen in these deep pictures has come from even farther away, so far away that the light has taken about 10 billion years to reach us!! This is close to the estimated age of the Universe and hence the deep pictures are probing not only out in distance but they probe back in time as well, since we can see galaxies as they appeared early in the history of the Universe. In this sense the deep pictures can be viewed as time machines allowing us to see deep into our past. The allow cosmologists directly to observe galaxies in the process of formation. Their theories can then be tested in detail.
The ability to detect galaxies at redshifts as high as z=6 comes from the new red and near-IR Hubble and Herschel deep pictures. Essentially they allow much more accurate measurements of the colours of the faintest galaxies, and the quality of these measurements is so high that the galaxy colours become a very good substitute for galaxy spectra and this allows new estimates of the galaxy redshifts to be obtained.
Could we detect galaxies at even higher redshifts?
The detection of bright galaxies at z=4-6 opens up the question as to whether galaxies at even higher redshift may exist. Though it would make even more problems for theorists, the timespan between z=10 or z=20 and z=5 is incredibly short relative to the timespan between z=5 and z=0. To observe galaxies at these redshifts we need even deeper pictures over a relatively wide field, particularly at infra-red wavebands. The new Wide Field Camera at the UK Infrared Telescope on Hawaii and the UK VISTA telescope in Chile which will be available in a few years will open up these new redshift regimes for observation. A few years later the giant NASA-ESA 6.5-metre Next Generation Space Telescope (NGST) in which the UK has a share will be launched to observe even deeper and further into the infrared with the prime aim of detecting at the highest redshifts the dawn of the age of the galaxies.
The Durham Cosmology Group.
The members of the Durham research team are Tom Shanks (Reader), Nigel Metcalfe (Computer Officer), Dick Fong (Sen. Lecturer), and Geoff Busswell (PhD student). The Durham Cosmology group has been active in the Deep Imaging/Galaxy Counts area since 1976. The group is very experienced in the techniques of measuring the light from faint galaxies as the group has led the way in faint galaxy research, first using machine measured photographs to take detect galaxies at the B=20-24 mag limits in the period (1976-1984). They then used electronic CCD detectors on 4 metre ground-based telescopes in the period (1985-1996) and most recently using the Hubble Space Telescope data , to probe from B=25 mag to B=29 mag. The group is also highly experienced in the techniques of modelling the counts and colours of the faint galaxies detected in these deep images.
The Deep Pictures.
Hard copies of the deep pictures, in colour, from the William Herschel Telescope, the Calar Alto Telescope and the Hubble Space Telescope can be obtained from Tom Shanks.
This press release and the deep pictures, and instructions as to how to obtain the paper, will be shown on the world-wide web site (after 8th August):
http://star-www.dur.ac.uk/cosmology/pressrelease.html
