South Pole Telescope

The South Pole Telescope (SPT) is a 10-meter (394 in) diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (CMB). The first major survey with the SPT–designed to find distant, massive, clusters of galaxies through their interaction with the CMB, with the goal of constraining the dark energy equation of state–was completed in October 2011. In early 2012, a new camera (SPTpol) was installed on the SPT with even greater sensitivity and the capability to measure the polarization of incoming light. This camera operated from 2012–2016 and was used to make unprecedentedly deep high-resolution maps of hundreds of square degrees of the Southern sky. In 2017, the third-generation camera SPT-3G was installed on the telescope, providing nearly an order-of-magnitude increase in mapping speed over SPTpol. The South Pole Telescope (SPT) is a 10-meter (394 in) diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (CMB). The first major survey with the SPT–designed to find distant, massive, clusters of galaxies through their interaction with the CMB, with the goal of constraining the dark energy equation of state–was completed in October 2011. In early 2012, a new camera (SPTpol) was installed on the SPT with even greater sensitivity and the capability to measure the polarization of incoming light. This camera operated from 2012–2016 and was used to make unprecedentedly deep high-resolution maps of hundreds of square degrees of the Southern sky. In 2017, the third-generation camera SPT-3G was installed on the telescope, providing nearly an order-of-magnitude increase in mapping speed over SPTpol. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the Fermi National Accelerator Laboratory. It is funded by the National Science Foundation and the Department of Energy. The South Pole is the premier observing site in the world for millimeter-wavelength observations. The Pole's high altitude (2.8 km/1.7 mi above sea level) means the atmosphere is thin, and the extreme cold keeps the amount of water vapor in the air low. This is particularly important for observing at millimeter wavelengths, where incoming signals can be absorbed by water vapor, and where water vapor emits radiation that can be confused with astronomical signals. Because the sun does not rise and set daily, the atmosphere at the pole is particularly stable. Further, there is no interference from the sun in the millimeter range during the months of polar night. The telescope is a 10-meter (394 in) diameter off-axis Gregorian telescope in an altazimuth mount (at the poles, an altazimuth mount is effectively identical to an equatorial mount). It was designed to allow a large field of view (over 1 square degree) while minimizing systematic uncertainties from ground spill-over and scattering off the telescope optics. The surface of the telescope mirror is smooth down to roughly 25 micrometers (one thousandth of an inch), which allows sub-millimeter wavelength observations. A key advantage of the SPT observing strategy is that the entire telescope is scanned, so the beam does not move relative to the telescope mirrors. The fast scanning of the telescope and its large field of view makes SPT efficient at surveying large areas of sky, which is required to achieve the science goals of the SPT cluster survey and CMB polarization measurements. The first camera installed on the SPT contained a 960-element bolometer array of superconducting transition edge sensors (TES), which made it one of the largest TES bolometer arrays ever built. The focal plane for this camera (referred to as the SPT-SZ camera because it was designed to conduct a survey of galaxy clusters through their Sunyaev–Zel'dovich effect signature) was split into six pie-shaped wedges, each with 160 detectors. These wedges observed at three different frequencies: 95 GHz, 150 GHz, and 220 GHz. The modularity of the focal plane allowed it to be broken into many different frequency configurations. For the majority of the life of the camera, the SPT-SZ focal plane had one wedge at 95 GHz, four at 150 GHz, and one at 220 GHz. The SPT-SZ camera was used primarily to conduct a survey of 2500 square degrees of the Southern sky (20h to 7h in right ascension, −65d to −40d declination) to a noise level of roughly 15 micro-Kelvin in a 1-arcminute pixel at 150 GHz.