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Open Access Publications from the University of California

A polarization sensitive bolometer array for the South Pole Telescope and measurements of Cosmic Microwave Background secondary anisotropies

  • Author(s): George, Elizabeth Marie
  • Advisor(s): Holzapfel, William L.
  • et al.

Over the past several decades, measurements of the Cosmic Microwave Background (CMB) have been a major driving force in our understanding of cosmology. Measurements of the CMB on large angular scales places tight constraints on the parameters of the Lambda-CDM cosmological model. Measurements of the CMB at smaller angular scales constrains secondary anisotropies, such as the thermal and kinetic Sunyaev Zel'dovitch (tSZ and kSZ) effects, which constrain the structure of the universe at later times. The CMB is also polarized, and the polarization signal encodes information about both the inflationary era and late-time structure formation in our universe. In the first part of this dissertation, I introduce the CMB and discuss the measurements that have been made so far and what we can learn from them.

The South Pole Telescope (SPT) is a 10 meter telescope that is dedicated to measuring the CMB down to small angular scales. So far, the SPT has housed two instruments, SPT-sz and SPT-pol. SPT-sz was sensitive to temperature and completed a 2540 square degree survey of the southern sky from 2008-2011. SPT-pol is a polarization sensitive camera that was deployed in 2012, and has been conducting a polarization survey since that time. These instruments both use photon-noise limited superconducting Transition Edge Sensors (TESes) in large numbers to obtain their high sensitivities. TES design and fabrication in large format arrays was critical to the success of these instruments. The second part of this dissertation focuses on the instrumentation of the SPT. I present the theory behind TES bolometer design with a focus on detector stability and optimal performance. Finally, I discuss the design and performance of the two instruments, with a focus on the detector development for the SPT-pol instrument.

In the final part of this dissertation, I use the full 2540 square degree SPT-sz survey to measure the power spectrum from 1850 < l < 11000 at 90, 150, and 220 GHz and constrain small scale CMB anisotropies. We use a multifrequency cross-spectrum analysis to fit the data using a model that includes the lensed primary CMB, secondary CMB anisotropies (tSZ and kSZ effects), and foregrounds. The foreground power consists of a poisson component from radio sources, poisson and clustered components from dusty point sources, galactic cirrus, and tSZ-CIB correlations. These data represent the most sensitive measurement of the small angular scale CMB power spectrum to date. The data constrain the amplitude of the tSZ and kSZ signals, from which we can learn about late time structure and the epoch of reionization.

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