|Cosmic Background Imager|
The Cosmic Background Imager (CBI) is an instrument designed to make images of the cosmic microwave background radiation and to measure its statistical properties on angular scales from 5 arc minutes to one degree (spherical harmonic scales from l = 3000 down to l = 300).
The CBI is a 13-element interferometer mounted on a 6 meter platform operating in ten 1-GHz frequency bands from 26 GHz to 36 GHz. The instantaneous field of view of the instrument is 44 arcmin and its resolution ranges from 4.5 to 10 arcmin.
The spectral capabilities of the CBI can be used to look for and separate diffuse foreground synchrotron, free-free, and dust emission from the interstellar medium in our Galaxy. Unresolved extragalactic sources are measured with the 40 meter telescope at the Owens Valley Radio Observatory, and subtracted from the CBI images.
The CBI is also a powerful instrument for observing the Sunyaev-Zel'dovich scattering of background radiation photons by the hot electrons in clusters of galaxies. Measurements of this effect can be used to study the properties of the hot cluster gas and the evolution of clusters, and to measure the Hubble constant directly.
The CBI is located at an altitude of 5080 meters near San Pedro de Atacama, in northern Chile. A high, dry site is essential in order to reach the required sensitivity levels in a reasonable observing time.
Following extensive tests on the campus of the California Institute of Technology in Pasadena, California, the CBI was shipped to Chile in August 1999 and has been making observations of the microwave background since November 1999.
The CBI shares many design elements with DASI, an interferometer that probes larger angular scales. DASI is currently making observations from the Amundsen-Scott South Pole station.
See also our technical papers on the CBI.