Atacama Cosmology Telescope

The Atacama Cosmology Telescope (ACT) is a 6-meter microwave telescope on the Atacama Desert at an altitude of 5190 meters, deployed in 2007 to survey the cosmic microwave background (CMB). Its aim has been to identify distant galaxy clusters using the Sunyaev-Zel'dovich effect, e.g., for further study using SDSS data, and to gather polarization information useful for cosmology studies.

Its current series of receivers introduced in 2015, called AdvACT (for Advanced ACTPol), are arrays of transition edge sensor (TES) bolometers that have covered bands ranging from 27 GHz to 230 GHz, with up to 1.4 arcmin angular resolution. Earlier series of receivers covered a smaller frequency range, the original series, called MBAC (Millimeter Bolometer Array Camera), with three 32 × 32 grids, for 145 GHz, 215 GHz and 280 GHz. In 2013, MBAC was replaced by the ACTPol series of receivers, which sense CMB polarization, including receivers covering 97 GHz and 148 GHz, with each bolometer sensitive to polarization.

The instruments are designed for surveying, i.e., coverage of survey fields of hundreds to thousands of square degrees, the surveys sometimes referred to as the ACT Survey, the ACTPol Survey, and the AdvACT Survey. As the telescope is located in Chile, the coverage is generally in the southern hemisphere. Survey locations were chosen so as to provide coverage complementary to that of some visible light surveys.