Distant star bursts provide key to the origin of galaxies

September 17, 2003

Revealing images produced by one of the world's most sophisticated telescopes are enabling a team of Edinburgh astronomers to see clearly for the first time how distant galaxies were formed 12 billion years ago. Scientists from the UK Astronomy Technology Centre (UK ATC) and the University of Edinburgh have been targeting the biggest and most distant galaxies in the Universe with the world's most sensitive submillimetre camera, SCUBA. The camera, built in Edinburgh, is operated on the James Clerk Maxwell Telescope in Hawaii. The images, published in Nature tomorrow (18 September), reveal prodigious amounts of dust-enshrouded star formation which could ultimately tell scientists more about the formation of our own galaxy.

It is thought these distant galaxies in the early Universe will evolve into the most massive elliptical galaxies seen at the present day. These giant galaxies consist of 1000 billion stars like our Sun and are found in large groups or clusters.

Dr. Jason Stevens, astronomer at the UK ATC in Edinburgh explained why understanding the evolution of these galaxies is so important. "The distant, youthful Universe was a very different place to the one we inhabit today. Billions of years ago, massive galaxies are thought to have formed in spectacular bursts of star formation. These massive elliptical galaxies have relatively simple properties. We hope that by understanding how simple galaxies form we will be one step closer to understanding how our own, spiral, Milky Way galaxy formed".

Prof. Jim Dunlop, Head of the University of Edinburgh's Institute for Astronomy said: "For a long time astronomers have anticipated that the formation of the most massive galaxies should have been a spectacular event, but failed to find any observational evidence of massive galaxy formation from optical images. Now we have discovered that it is indeed spectacular, but because of the effects of interstellar dust, the spectacle is only revealed at submillimetre wavelengths." The dust absorbs the bright blue light emitted by young stars. The energy from the light heats the dust and makes it glow. It is this glow that is detected by the SCUBA camera.

Dr. Stevens and his colleagues suspected that these massive galaxies would form in particularly dense regions of space so they chose regions of very distant space that are known to be very dense because they contain massive radio galaxies - galaxies which emit high levels of radio waves. They found that many of the radio galaxies have near-by companion objects that had not previously been detected at any wavelength. Dr. Rob Ivison, also at the UK ATC, described what they found. "The companion objects are located in the densest parts of the intergalactic medium, strung out like beads of water on a spider's web due to the filamentary structure of the Universe".

The SCUBA images support a popular current model of galaxy formation in which today's massive elliptical galaxies were assembled in the early Universe in dense regions of space through the rapid merging of smaller building blocks.

The images are available here at http://www.pparc.ac.uk/Nw//Press/embargoed_images.asp. They are password protected until 18:00 17 September 2003. The user name is 'press' and the password is 'silicrete'.

1. The SCUBA images. These images show massive galaxies caught in the throes of formation. The stars are forming so rapidly that an entire galaxy can be built in a short timescale (cosmologically speaking, so a billion years or so). The star formation in these galaxies is thought to be driven by mergers of older galaxies in a filamentary structure spanning millions of light years. In billions of years time, this structure is predicted to become a cluster of giant elliptical galaxies similar to those we see today in the local Universe.

The images were taken with the SCUBA camera at the James Clerk Maxwell Telescope at a wavelength of 0.85 mm. The radiation detected comes from a massive amount of small grains of cosmic dust made of carbon and silicate that glow because they are heated by blue light from hot young stars. Each image is centred on a distant Radio Galaxy. A radio galaxy is so called because it emits jets of high speed plasma that originate close to a massive black hole at its centre, and emit strongly at radio wavelengths - the tick marks in the image show the direction of these jets.

From left to right and top to bottom the images are centred on the following radio galaxies: 4C41.17, 4C60.07, 8C1435+635, 8C1909+722, B3J2330+3927 and PKS1138-262.

2. Abell 2218. This is an optical image taken with the Hubble Space Telescope which shows a cluster of massive elliptical galaxies. This cluster illustrates what the forming galaxies will eventually look like. Photo credit: NASA

3. The James Clerk Maxwell Telescope. Photo credit: Royal Observatory, Edinburgh

4. Summit of Mauna Kea, a 14000ft dormant volcano on the Big Island, Hawaii. The James Clerk Maxwell Telescope can be seen down in the valley in the centre of the picture. Photo credit: Image courtesy of the James Clerk Maxwell Telescope, Mauna Kea Observatory, Hawaii


How do astronomers look back in time?

The further light has to travel across the universe before it reaches the earth, the longer it takes to get here. That may sound obvious but it is very useful for astronomers. It means that when they look at objects in the furthest reaches of the universe, the light which is captured by the telescope and camera has taken most of the age of the universe to reach the earth. In other words they are also looking back in time to how the universe was shortly after it formed.

However, it is not as easy as it sounds. On its way across the universe the light becomes stretched (because the universe is expanding) so that when it reaches the earth it is at much longer wavelengths than it was when it was originally emitted. This is known as 'red-shift'.

The light from the star-forming galaxies in this study has been stretched so much that it has been shifted from the far-infrared waveband, accessible only from space, to the submillimetre waveband. Submillimetre radiation is emitted in the region of the electromagnetic spectrum which lies between infrared light and radio waves. Because it is absorbed by water vapour in the atmosphere it can only be detected from the Earth's highest mountains - in this case the 14,000ft Mauna Kea on Hawaii. The radiation that we detect is predominantly produced by a population of young hot young stars. This star-light is absorbed by small grains of graphite and silicate - 'interstellar dust' - and is re-radiated at longer far-infrared and submillimetre wavelengths.

The James Clerk Maxwell Telescope (JCMT) The JCMT is the world's largest single-dish submillimetre telescope. It collects faint submillimetre signals with its 15 metre diameter dish. It is situated near the summit of Mauna Kea on the Big Island of Hawaii, at an altitude of approximately 4000 metres (14000 feet) above sea level. It is operated by the Joint Astronomy Centre, on behalf of the UK Particle Physics and Astronomy Research Council, the Canadian National Research Council, and the Netherlands Organisation for Scientific Research.

SCUBA (the Submillimetre Common-User Bolometer Array) is the world's most powerful submillimetre camera. It is attached to the James Clerk Maxwell Telescope, and contains sensitive detectors called bolometers, which are cooled to 60 milliKelvin, 0.06 degrees above absolute zero (60 milliKelvin is about -273.1 Celsius, -459.6 Fahrenheit). SCUBA was built in the UK by the Royal Observatory, Edinburgh, at what is now the UK Astronomy Technology Centre.

The UK Astronomy Technology Centre is located at the Royal Observatory, Edinburgh (ROE). It is a scientific site belonging to the Particle Physics and Astronomy Research Council (PPARC). The mission of the UK ATC is to support the mission and strategic aims of PPARC and to help keep the UK at the forefront of world astronomy by providing a UK focus for the design, production and promotion of state of the art astronomical technology.

The Royal Observatory, Edinburgh comprises the UK Astronomy Technology Centre (UK ATC) of the Particle Physics and Astronomy Research Council (PPARC), the Institute for Astronomy (IfA) of the University of Edinburgh and the ROE Visitor Centre.

The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Southern Observatory and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.
Eleanor Gilchrist
44-0-131-668 -8397
PR Officer, ROE

Dr. Jason Stevens
Astronomer, UK ATC

Dr. Rob Ivison
Astronomer, UK ATC

Professor Jim Dunlop 44-0-131-668-8349
Head of the Institute for Astronomy

Julia Maddock
Press Officer, PPARC

Ronald Kerr
Press Officer, University of Edinburgh

Douglas Pierce-Price
Outreach Officer, Joint Astronomy Centre



Science and Technology Facilities Council

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