Extragalactic Astronomy and Cosmology

The UK ATC extragalactic astronomy and cosmology group comprises Dr Rob Ivison, Dr Jason Stevens, Thomas Greve, a final-year student at the IfA, Dr Gillian Wright and Prof. Ian Robson.

Almost all of the research undertaken by the group is observational in nature, primarily in the infrared, submillimetre and radio wavebands, though we also work with X-ray and optical data when the need arises.

Our group was largely responsible for the discovery of the so-called `SCUBA' or `submm' galaxy population, using the Edinburgh-built SCUBA submm camera in 1997-8. The first deep images taken with SCUBA, using distant galaxy clusters as cosmological lenses, revealed a hitherto unknown population of dusty, starburst galaxies. This was soon confirmed via an extraordinary submm image of the Hubble Deep Field. See the images below:

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Left: The first deep extragalactic image taken using the SCUBA submm camera, using the Abell 370 galaxy cluster to amplify distant star-forming galaxies. The bright source to the south (`Le Blob') was quickly found to be a gas-rich hyperluminous galaxy at z=2.8 containing an active galactic nucleus (Smail et al. 1997, ApJ, 490, L5).

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Right: The second deep extragalactic image taken using the SCUBA submm camera, through the Abell 1835 galaxy cluster which can be seen as a group of yellow and orange galaxies in the foreground. The SCUBA emission (largely from even more luminous background galaxies) is shown as contours (Ivison et al. 2000, MNRAS, 315, 209).

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Above: Multi-wavelength pictures of the first galaxy detected by SCUBA - `Le Blob', aka SMM J02399-0136 (Ivison et al. 1998, MNRAS, 298, 583).

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Above: The discovery images that showed that many submm galaxies are associated with extremely red objects (EROs) - galaxies so red that they appear only in infrared images, being 100x brighter at 2 microns than in the visible bands due to the obscuring effects of cosmic dust (Smail et al. 1999, MNRAS, 308, 1061.

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Above: High-resolution images of the second galaxy detected by SCUBA, SMM J14011+0252, a gas-rich ultraluminous starburst at z=2.56. The upper central image is from the Hubble Space Telescope, showing the complex morphology (due partly to the gravitational lens in the foreground). The lower images show the radio emission as contours (right panel), and the emission from CO tracing the molecular gas (left panel) (Ivison et al. 2001, ApJ, 561, L45).

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Left: Extraordinarily deep submm image of the Hubble Deep Field (North), taken with SCUBA during the El Nino winter of early 1998 (Hughes et al. 1998, Nature, 394, 241).

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Right: The Very Large Array in New Mexico - one of the telescopes used most often by our group.

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Left: The James Clerk Maxwell Telescope on Mauna Kea, Hawaii - the telescope on which the SCUBA camera operates.

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Our goal is to understand the formation and evolution of these galaxies, and to this end we have concentrated in recent years on determining their properties using facilities such as the Very Large Array, the mighty Keck telescope on Mauna Kea, the UKIRT, the Hubble Space Telescope and the XMM-Newton X-ray observatory in space.

We have found that 2/3rds of the galaxies can be pinpointed accurately in deep radio images via the emission from supernova remnants and/or active galactic nuclei and that, once pinpointed in this way, they are often associated with extremely red objects (EROs) or composite blue/red sources with complex morphologies. Follow-up spectroscopy with Keck has indicated a median redshift of at least 2.4 (a look-back time of around 10 billion years), in agreement with estimates from the ratio of their submm-to-radio fluxes.

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Right: The distant radio galaxy, 8C1909+72, as imaged by SCUBA, showing the merger-like morphology associated with the radio galaxy, and another bright starburst to the south (Stevens et al. 2003, Nature, 425, 264).

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In more recent times, we have broadened the scope of these investigations in an attempt to better understand the interdependency of star formation and the growth of super-massive black holes in active galactic nuclei, targeting X-ray-selected samples with SCUBA. We are also working towards an understanding of the growth of galaxy clusters, and the formation of the very dust that SCUBA sees.

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Left: SCUBA image of the Cas A supernova remnant. The emission evident in this image finally explains the origin of dust in the early Universe. It had been a mystery how so much processed material could have been created so quickly until SCUBA showed that several solar masses of dust can be created in a supernova explosion - the remnant of a star that lives fast and dies young (Dunne et al. 2003, Nature, 424, 285).

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Full lists of our refereed publications can be found by clicking on the relevant author: Ivison, Greve, Wright, Robson.

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The Royal Observatory Edinburgh comprises the UK Astronomy Technology Centre of the Science and Technology Facilities Council, the Institute for Astronomy of the University of Edinburgh and the ROE Visitor Centre.