UK astronomers Elizabeth Stanway, Andrew Bunker and Richard McMahon at the
Institute of Astronomy, University of Cambridge, England, have used three of
the most powerful telescopes in existence to identify some of the farthest
galaxies yet seen. But at the same time, they have encountered a cosmic
conundrum: it looks as if there were fewer galaxies forming stars at this
early stage in the history of the Universe than in the more recent past.
Their results, which will be published in the Monthly Notices of the Royal
Astronomical Society, show for the first time, that astronomers may be
probing back to the era when the first stars and galaxies were forming.

Stanway, Bunker and McMahon used the unique power of the Hubble Space
Telescope and analysed publicly-available images taken in the direction of
the southern hemisphere constellation of Fornax (the Oven) with the new
Advanced Camera for Surveys as part of the ‘Great Observatory Origins Deep
Survey’ (GOODS) project. They identified half a dozen objects likely to be
galaxies 95 per cent of the way across the observable Universe. The
redshifts of these galaxies are about 6 and they are so far away that
radiation from them has taken about 13 billion years to reach us. They
existed when the Universe was less than a billion years old and seven
billion years before the Earth and Sun formed. Intervening gas clouds
absorbed visible light from them long before it reached Earth but their
infrared light can be detected – and it is their infrared ‘colours’ which
lead the researchers to believe that they lie at such immense distances.

They also used infrared images taken with one of the 8-metre telescopes
forming the Very Large Telescope (VLT) at the European Southern Observatory
(ESO) in Chile to study these galaxies. “The ESO pictures allowed us to
distinguish very distant galaxies at the edge of the observable Universe
from objects nearby,” said graduate student Elizabeth Stanway, who has
identified the galaxies as part of her research for a doctorate in
astrophysics at Cambridge.

Having drawn up a list of objects that could be remote galaxies, the
astronomers then turned to one of two Keck telescopes, which are the largest
in the world and are at the top of the 14000ft mountain of Mauna Kea in
Hawaii. Working with California astronomers Professor Richard Ellis
(Caltech) and Dr Patrick McCarthy (Carnegie Observatories) they took a
spectrum of one of them. They saw the signature of hydrogen gas glowing as
it is illuminated by hot, newly-born stars, and measured the redshift to be
5.78. “This galaxy is in the process of giving birth to stars – each year it
converts a mass of gas more than 30 times that of our Sun into new stars”,
according to research astronomer Dr. Andrew Bunker. These additional results
have recently been submitted to the Monthly Notices of the Royal
Astronomical Society.

“Using the Keck, was very important as it showed that this population of
objects discovered by the Hubble Space Telescope really is incredibly
distant”, said Andrew Bunker, who was part of the team which did the
observing in Hawaii. “The galaxy we have proved to be very distant is only
1000 light years across. This is very small compared to our own galaxy, the
Milky Way, which is 100 times larger” added Elizabeth Stanway.

But the Cambridge team have also found a cosmic puzzle: on the basis of
their sample, they can calculate how may galaxies there are involved in the
rapid formation of stars in the very distant universe (redshift 6). They
have compared the answer with previous work looking at nearer galaxies, with
redshifts around 4. It seems that there are fewer of these galaxies early in
the history of the Universe, compared to more recent times.

Theoretical predictions for the star formation history of the universe are
highly uncertain, which is why this observational work is essential. “It
could be that we are seeing some of the first galaxies to be born”, said
Richard McMahon, “The light from these first stars to ignite could have
ended the Dark Age of the Universe as the galaxies ‘turn on’, and might have
caused the gas between the galaxies to be blasted by starlight – the
‘reionization’ which has recently been detected in the cosmic microwave
background by the WMAP satellite”. The results of the Cambridge group
combined with the recent results from WMAP satellite complement each other
and show that the Dark Age ended sometime between 200 and 1000 million years
after the Big Bang with the formation of the first stars.

This team of astronomers are currently building a new instrument in
Cambridge called ‘DAZLE’, which will probe even earlier in the history of
the Universe and shed new light on the ‘Dark Ages’.

CONTACTS

Elizabeth Stanway, email: ers@ast.cam.ac.uk, Tel: +44-(0)1223-337531

Dr Richard McMahon, email: rgm@ast.cam.ac.uk, Tel: +44-(0)1223-337519

Dr Andrew Bunker, email: bunker@ast.cam.ac.uk, Tel: +44-(0)1223-339071
(only available by e-mail 10-26 March)

NOTES

1. Images to go with this release available from

http://www.ast.cam.ac.uk/~bunker/internal/CambridgeGOODS/

2. Details of the scientific papers

“Lyman Break Galaxies and the Star Formation Rate of the Universe at z~6” by
Elizabeth Stanway, Andrew Bunker and Richard McMahon. Accepted for
publication by Monthly Notices of the Royal Astronomical Society

See http://xxx.lanl.gov/abs/astro-ph/0302212

“A star-forming galaxy at z=5.78 in the Chandra Deep Field South” by Andrew
Bunker, Elizabeth Stanway, Richard Ellis, Richard McMahon and Patrick
McCarthy. Submitted for publication in Monthly Notices of the Royal
Astronomical Society.

See http://xxx.lanl.gov/abs/astro-ph/0302401

3. Useful internet resources:

Insitute of Astronomy, Cambridge http://www.ast.cam.ac.uk

Caltech Astronomy Department http://www.astro.caltech.edu

Observatories of the Carnegie Institute of Washington http://www.ociw.edu

Space Telescope Science Institute http://www.stsci.edu

Great Observatory Origins Deep Survey (GOODS)
http://www.stsci.edu/ftp/science/goods

European Southern Observatory – Very Large Telescope
http://www.eso.org/instruments

Keck Observatory http://www2.keck.hawaii.edu

Dark Ages Z Lyman-alpha Explorer (DAZLE) http://www.aao.gov.au/dazle