Friday, October 23, 2009

First Results of SPT’s SZ Survey

On Saturday, October 10, the astronomy team managing the South Pole Telescope released the first results from their initial SZ survey. Wait. You didn’t know we had a telescope at the South Pole? It’s true. We do.

The SPT is a colaborative effort, supported by many U.S. universities and organizations, including the Jet Propulsion Laboratory (JPL), with most of the staff based at the University of Chicago. Located at the Amundsen-Scott South Pole Station, the SPT was constructed between November 2006 and February 2007, and saw first light on February 16.

The largest telescope deployed at the South Pole, the SPT stands 22.8 meters tall and has a 10-meter dish covered with a network of detectors. Like a few other cutting-edge programs, including the ESA/NASA Planck mission, SPT is studying cosmic microwave background radiation (CMBR), the afterglow of the Big Bang. On the electromagnetic spectrum, CMBR falls somewhere between heat radiation and radio waves. The CMBR is mostly uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters that are visible today.

One advantage of the SPT location is the darkness. The months of darkness during the South Pole winter gives ample opportunities for exploring the skies, and the desolate location ensurse that light pollution from buildings and streetlamps is of little concern. Dry, cold air allows CMBR to be observed with minimal interference from water vapor.

Another advantage of the locating at the South Pole is that the observed celestial bodies do not set, but instead rotate once every 24 hours around celestial north. This allows the scientists to track on a point in the sky for months or even years. This is in contrast to the middle latitudes where stars eventualy dip below the horizon after a few hours.

The SPT is currently conducting a Sunyaev-Zel'dovich (SZ) effect survey over large areas of the southern sky, searching for massive galaxy clusters to high redshift. The SZ effect is the result of high energy electrons distorting the CMBR through a phenomenon called inverse Compton scatting. In their preliminary study, the team is focusing on a 40 square-degree area targeted by the Blanco Cosmology Survey (BCS). Over two seasons of observations, the region has been mapped by the SPT at frequencies of 95 GHz, 150 GHz, and 225 GHz.

On October 10, the team reported the four most significant detections of SZ-effected galaxy clusters in this field, three of which were previously unknown and, therefore, represent the first three galaxy clusters discovered with an SZ survey. The team is very excited about the latest results because they demostrate that SZ surveys can be an effective means of finding galaxy cluters. The results also show that the SPT is a very effective instrument for this type of study.

For more on the SPT and other CMBR-related missions, check out these links:

South Pole Telescope

Planck Mission, ESA Home Page

Planck Mission, NASA Home Page

NASA’s Legacy Archive for Microwave Background Data Analysis

NASA's Cosmic Background Explorer (COBE) Archive Page

NASA's Wilkinson Microwave Anisotropy Probe (WMAP) Archive Page

NASA's and the Netherlands (NIVR) Infrared Astronomical Satellite (IRAS) Archive Page


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