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RISS 인기검색어
- 검색키워드
- 저자 : Niemack, Michael D (검색결과 1 건)
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Towards dark energy: Design, development, and preliminary data from ACT
Niemack, Michael D Princeton University 2008 해외박사(DDOD)
Recent cosmological observations resulted in the surprising discovery that our universe is dominated by a dark energy, causing acceleration of the expansion of the universe. Understanding the dark energy (Λ) and the cosmic acceleration may require a revolution in our understanding of the laws of physics, and more precise data will be critical to this endeavor. The remainder of the universe is dominated by cold dark matter (CDM), while only ∼4% of the universe comprises baryonic matter. To improve our understanding of dark energy and the ΛCDM model of our universe, we have developed a novel telescope and receiver technology to map the universe at millimeter wavelengths on arcminute angular scales. The Atacama Cosmology Telescope (ACT) and its receiver, the Millimeter Bolometer Array Camera (MBAC), are optimized to measure temperature anisotropies in the primordial cosmic microwave background radiation (CMB). On the smallest angular scales measured by ACT the anisotropies are dominated by secondary interactions of CMB photons, such as gravitational interactions and the Sunyaev-Zel'dovich (SZ) effects: the interaction of CMB photons with ionized gas in galaxy clusters. We can use these measurements to probe dark energy in multiple ways. The CMB bispectrum quantifies the non-Gaussian nature of the secondary anisotropies and when combined with measurements from the Wilkinson Microwave Anisotropy Probe, will provide constraints on dark energy. By combining and cross-correlating measurements of the SZ effects with galaxy cluster redshifts, we can constrain the equation of state of dark energy and its evolution. In addition, by measuring the CMB on arcminute angular scales, we will probe the details of the ΛCDM cosmological model that describes our universe. This dissertation begins with the development of the optical designs for ACT and MBAC that focus light onto the MBAC bolometer arrays. The kilo-pixel bolometer arrays are the largest ever used for CMB observations. The arrays utilize superconducting transition edge-sensor (TES) bolometers to measure changes in optical power, which are coupled to superconducting quantum interference devices (SQUIDs) for signal measurement and amplification. A model describing the functionality of the TES bolometers is presented in addition to a procedure developed to characterize all bolometers before assembling them into arrays. The capabilities and characterization of the time-domain SQUID multiplexing readout system and electronics are discussed, including the implications of magnetic sensitivity for the readout system and recently developed array characterization techniques. Measurements of the first fully-assembled detector array are presented, including: functionality, efficiency, detector time constants, and noise. Preliminary results from the first season of CMB observations are also discussed. A new approach for measuring photometric redshifts of galaxies using optical and ultraviolet observations is presented. These photometric redshifts will be cross-correlated with SZ cluster measurements from ACT to improve our understanding of dark energy. Finally, predictions are given for the sensitivity of the experiment from both one and two seasons of observations.
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