Observations with the APEX Sunyaev-Zel'dovich experiment

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AST-0709497LeeThis project will carry out a deep blind survey for galaxy clusters via the Sunyaev-Zel'dovich effect (SZE), using the Atacama Pathfinder EXperiment (APEX) telescope and a 320-element superconducting bolometer array. This involves a close collaboration with the Max Planck Institute for Radioastronomy (MPIfR, Bonn, Germany). A high-quality catalog of SZE-selected clusters over a broad range of redshifts will provide deep insight into structure formation, high accuracy measurements of cosmological parameters, and a characterization of the dark energy equation of state. This dark energy measurement is complementary in parameter degeneracies to other types, such as those using supernovae. SZE surveys are expected to have a cleaner selection function that extends to higher redshift than optical and X-ray techniques. Hundreds of galaxy clusters will be detected, with as many as one hundred at redshift one or greater.APEX is a fully operational 12-meter diameter on-axis Cassegrain telescope sited at 16,700 ft on the Chajnantor plateau in Chile. It was built by a consortium of the MPIfR, the European Southern Observatory (ESO), and the Swedish Onsala Space Observatory. The SZE survey will use at least one month of telescope time per year, and this allotment may increase. The receiver has had a successful engineering run and been upgraded to the observational configuration. This program leverages the substantial investments in receiver development and deployment, in superconducting transition edge sensors (TES), and in construction and operation of the telescope, by NSF and by the various national and international partners.The planned calibration of the mass to SZE flux relation by APEX in an early emphasis project will be critical for interpreting the large cluster samples expected from future surveys by other telescopes. This will be carried out using multi-wavelength data from a variety of experiments all looking at the same patch of sky, and comparing the SZE data against measurements using optical weak lensing, optical galaxy counts, X-ray flux, and velocity dispersions. The work will cement relations across a strong international team. In addition, the detector development work has widespread implications for astronomy, other physics communities, and homeland security.