AMI will combine a large field of view with high sensitivity to faint objects, making it ideal for surveying the sky for the imprints of galaxy clusters on the microwave background. Optical and X-ray telescopes that search for clusters of galaxies are hampered by the fact that the clusters get fainter with increasing distance. It is therefore very difficult to find the most distant clusters that would tell us about the formation of structure in the universe. Different theories predict hugely different numbers of distant clusters. AMI will be able to count these clusters and thus determine which theory is correct.

Simulated AMI observation of about 1 square degree of sky, with a total observing time of 360 hours. In this model, in which the total mass density of the universe is equal to the critical density, large clusters form late in the history of the universe and there are relatively few distant clusters.	Identical simulation to the above, but with the density only 0.3 times the critical density. Now clusters form at earlier times and there are many distant clusters. The clusters that make these two simulations look different are all too distant to be found with optical or X-ray telescopes, but with AMI the difference is clear.
Cluster simulated data courtesy of Vince Eke, Institute of Astronomy, Cambridge

AMI will also be able to make high-resolution images of the SZ effect in relatively nearby clusters. In conjucntion with X-ray data this will allow detailed examination of the internal structure of the cluster gas, giving further clues to the way in which clusters form and grow.

Ryle Telescope observation of the rich cluster Abell 1914. This is an 84-hour observation with an existing telescope, showing a detection of the SZ effect but almost no resolution of its structure.	Simulated AMI observation of A1914 with the same observing time, showing vastly increased sensitivity and well-resolved structure in the cluster.

AMI will also have suficient sensitivity and resolution to detect the effect of cosmic strings on the CMB. Cosmic strings, which are predicted by unified field theories in particle physics, are line-like defects in the structure of space in which a high-energy state left over from the very early history of the universe is trapped and cannot decay to the low-energy state of the rest of space. They can be detected by the way they distort the background radiation as it passes moving strings. Detection of a cosmic string would have profound consequences for fundamental theories of physics. Only arcminute-scale observations will be able to distinguish cosmic strings from other features in the CMB.

Simulated image of the appearance of cosmic strings against the CMB. The characteristic positive-negative appearance is due to CMB photons being deflected from one side to the other of a moving string.	Simulated AMI observation of the same field. The sharp edges and positive-negative features are clearly detected.

Technical notes on the simulated images

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Last Modified 23 August 1999
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