This week I was meeting a colleague at the University of Chicago. We discussed about the point source contamination for the South Pole Telescope (See entry about
the visit in Jodrell Bank). The South Pole Telescope will be build under the leadership of John Carlstrom's group at University of Chicago.
The South Pole Telescope is a planned observation of clusters of galaxies, which will be deployed late 2006. It is a 10m telescope. The huge shield around it you can see in the image is to protect the telescope from the called 'ground spill', which are disturbing signals from the environment. The wavelength at which this telescope observes is in the mm and sub-mm regime. Observations at this wavelength require a very clean and stable atmosphere, which is given on the plateau of the South Pole which is at an altitude of 2800 m.
Now how does the South Pole Telescope 'observe' clusters of galaxies ?
The earth is reached from all around us by cosmic microwave background light. This is the light left over from the big bang. If this light travels through a cluster of galaxies its features (spectrum) gets changed by interacting with the intracluster gas. Basically what happens is that one receives a decreased (dependent on which part of the spectrum you are observing) flux of CMB photons compared to a region of space where there is no cluster.
This effect is called the Sunyaev-Zel'dovich effect. The beautiful thing is that it is independent of the distance of the cluster to the earth and hence one can potentially discover clusters of galaxies to huge distances.
Another time I will tell you how one can use these observations to learn more about dark energy ...