The story of galaxy evolution -- in full colour

Larry Klaes (
Fri, 06 Aug 1999 13:59:43 -0400

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>Date: Thu, 5 Aug 1999 08:13:46 -0700
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>Subject: The story of galaxy evolution -- in full colour
>Subject: The story of galaxy evolution -- in full colour (Forwarded)
>Date: Thu, 05 Aug 1999 19:08:46 -0400
>From: Andrew Yee <>
>Organization: via Internet Direct
>Royal Astronomical Society Press Notice
>Date: 5 August 1999
>Ref. PN 99/21 (NAM3)
>Issued by:
>Dr Jacqueline Mitton
>RAS Press Officer
>Phone: Cambridge ((0)1223) 564914
>FAX: Cambridge ((0)1223) 572892
>Cambridge astronomers are solving long-standing puzzles about how galaxies
>evolve by studying colour images from the Hubble Space Telescope of very
>remote galaxies. They have found strong evidence that galaxies grow when
>smaller clumps of stars and gas merge. They have also discovered that the
>bar structures seen at the centres of some spiral galaxies formed relatively
>Professor Richard Ellis and Dr Roberto Abraham (Institute of Astronomy,
>Cambridge) and Dr Nial Tanvir (now University of Hertfordshire), together
>with Cambridge graduate students Jarle Brinchmann and Felipe Menanteau
>have developed techniques to study, for the first time, the information
>available from the "internal" colours of distant galaxies revealed by the
>Hubble Deep Field. They are using the colours of the structures in the
>galaxies to gather information about the type and distribution of stars
>within the galaxies. Since these galaxies are very distant, we see them
>as they were long in the past, typically half the present age of the
>The results will be presented at the National Astronomy Meeting being held
>in Guernsey from the 10th to the 13th of August.
>Background and new results:
>Nearby galaxies come in three categories: spirals, characterised by their
>elegant swirling arms; ellipticals, which appear like smooth featureless
>collections of stars; and irregulars which have no symmetric structure.
>The Hubble Space Telescope is able to identify such galaxies to enormous
>distances [figure 1], corresponding to eras when the Universe was only half
>its current age. In earlier work, the team showed that many very distant
>(and hence young) galaxies do not resemble their present-day counterparts.
>The team has now developed powerful techniques to study the colours of
>structures INSIDE the galaxies (structures such as nuclei, central "bulges",
>and spiral arms, all of which show strikingly different colours, as seen in
>figure 1) in order to probe the age and chemical makeup of these distant
>galaxies. The aim is to understand the physical processes that govern the
>evolution of galaxies as well as how the peculiar star systems detected in
>Hubble Space Telescope images have evolved into the well-defined galaxy
>forms we see today.
>A popular theory claims that most elliptical galaxies formed from the
>collision of two spiral galaxies. In this scenario, the spiral arms are
>destroyed and the gaseous material is expelled or converted into stars.
>The Cambridge team has found striking evidence that distant ellipticals
>are varied in their internal colour properties [figure 2a], supporting the
>idea that merging has indeed taken place. This provides strong support
>for the theory that galaxies grow via the collisions of smaller structures.
>Their work has also addressed the history of spiral galaxies, such as our
>own Milky Way. A long-standing puzzle is why some of these systems have
>bar-like features in their centres [figure 2b]. By counting the fraction of
>barred and non-barred galaxies existing at different eras in the past, the
>Cambridge team (together with Professor Mike Merrifield at the University
>of Nottingham) have provided the first evidence that bars may be a relatively
>recent phenomenon. Few bars are found in the most distant spirals seen more
>than 5 billion years ago. (The age of the universe is thought to be about 12
>to 14 billion years.) This may be because bars develop as unstable features
>only when a spiral has grown to a certain size. This work has taken on added
>importance with the growing acceptance by astronomers that our own galaxy,
>The Milky Way, is also barred.
>The future is bright -- the future is infrared
>The next stage in understanding the evolution of galaxies will be directed
>towards studying the very faint peculiar galaxies discovered by the Hubble
>Space Telescope. A higher proportion of the galaxies in the deep Hubble
>pictures are of these amorphous types [labelled "peculiar" in figure 1] and
>astronomers have puzzled for several years over what has become of them
>at the present time. The make-up of these systems is difficult to study
>using the Hubble Space Telescope, because their peculiar appearance may
>arise partly from absorption by dust clouds in the galaxies. Fortunately a
>detailed understanding will soon become possible with the completion of
>two revolutionary new advances in ground-based telescope technology: the
>pair of Gemini telescopes, the first of which is now in operation in Hawaii,
>and one of its associated instruments called CIRPASS (the Cambridge
>Infrared PAnoramic Survey Spectrograph) now being built in Cambridge.
>The Gemini 8-m telescope on Mauna Kea, Hawaii (an international facility
>involving the United Kingdom) has already demonstrated its remarkable
>ability to study distant galaxies at infrared wavelengths with a resolution
>comparable to that of the Hubble Space Telescope. Working in the infrared
>effectively allows astronomers to look through the dust clouds that block
>visible light, providing data on the age and other properties of these
>Gemini's unique capabilities (its enormous light-gathering power because
>of its giant 8-m mirror, combined with ultra high-fidelity images) will be
>complemented by the unique spectroscopic mapping capabilities of CIRPASS
>which will provide the next stage in the internal colour study of galaxies.
>CIRPASS has been designed to take maximum advantage of Gemini's capacity
>to resolve distant galaxies and thus allows the study of their individual
>components. The instrument will further break down these colours into
>hundreds of detailed spectra [figure 3] distributed across the visible
>portions of the galaxies. Each spectrum can be used to study the rotation
>and chemical make-up of galaxies on a point-by-point basis for galaxy
>samples to enormous distances --- including those which formed soon
>after the Big Bang.
>Prof. Richard Ellis 01223-337516 (office), 0468-923277 (mobile),
>Dr Roberto Abraham 01223-766667 (office), 0467-371014 (mobile),
>Dr Nial Tanvir 01707 286299 (office),
>Prof. Michael Merrifield 0115 951-5186 (office), 0411 382612 (mobile) ,
>Except on Wednesday 11th August, please try press room numbers before
>calling mobiles.
>Press room phone numbers: 01481 710889, 01481 712834 and 01481 712936
>Press room fax number: 01481 713044.
>Mobile phone nos.:
>Jacqueline Mitton (RAS Press Officer): 0370-386133
>Peter Bond (RAS Press Officer, Space Science) : 0411-213486
>Charlotte Allen (PPARC Press Officer): 07899-945493
>Andrew Yee