A significant fraction of the Astrophysics Group is involved in work on the Cosmic Microwave Background, both experimental and theoretical. We are currently operating the Very Small Array, designed to image primordial CMB fluctuations on degree scales, building the Arcminute MicroKelvin Imager, an arcminute-scale survey telescope, and preparing analysis techniques for the forthcoming Planck satellite.

Over the last few years the detection of fluctuations in the CMB on degree scales and the measurement of their power spectrum has revolutionized observational cosmology. The Cosmic Anisotropy Telescope (CAT) was the first CMB telescope to detect structure in the microwave background radiation on angular scales smaller than the main peak in the power spectrum. The CAT was also the first interferometer to detect structures in the CMB, a technique now being used in several groups around the world. Our next generation instrument in this area, the Very Small Array (VSA), is now observing from its site in Tenerife. The VSA will be able to make images of the anisotropies on a range of angular scales between ~15 arcmin and 2 degrees. From this, it should be possible to deduce the density and age of the universe to a relative accuracy of about 10 percent.

On smaller angular scales, the main features visible in the CMB are due to clusters of galaxies, whose hot atmospheres scatter the CMB radiation via the Sunyaev-Zel'dovich effect. The Ryle Telescope was the first instrument able to make images of galaxy clusters via the SZ effect. This information enables us to measure the Hubble constant and to search for proto-clusters forming at very high redshift. Gravitational-lensing inversion techniques are also being developed to compare the total mass in clusters to the gas mass measured via the SZ effect. The next project in this field is the Arcminute MicroKelvin Imager (AMI), which will be able to detect high-redshift clusters and proto-clusters over large areas of sky, as well as search for fine structures in the primary CMB anisotropies due to, for example, re-ionization or cosmic strings. AMI is being built at the moment and is expected to begin observing early in 2003. As well as making several surveys which will be made public as soon as possible, AMI will be available to guest observers - details of the application procedure will be published when the telescope is nearing completion.

Future plans include involvement in observations of the 2.7-K background from space, which will be made by the European Planck Surveyor satellite due for launch in 2007. The Cambridge Planck Analysis Centre is a designated centre for scientific analysis for this satellite, and data analysis techniques for this mission are already under intensive development in the Astrophysics Group.

Last Modified 11 January 2002
Please send comments to Mike Jones.