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Register a new userMultichroic TES Bolometers and Galaxy Cluster Mass Scaling Relations with the South Pole Telescope
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Benjamin Saliwanchik
Publication date
2016
fields
Physics
and research's language is
English
Authors
Benjamin Saliwanchik
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The South Pole Telescope (SPT) is a high-resolution microwave-frequency telescope designed to observe the Cosmic Microwave Background (CMB). To date, two cameras have been installed on the SPT to conduct two surveys of the CMB, the first in intensity only (SPT-SZ) and the second in intensity and polarization (SPTpol). A third-generation polarization-sensitive camera is currently in development (SPT-3G). This thesis describes work spanning all three instruments on the SPT. I present my work in time-reversed order, to follow the canonical narrative of instrument development, deployment, and analysis. First, the development and testing of novel 3-band multichroic Transition Edge Sensor (TES) bolometers for the SPT-3G experiment is detailed, followed by the development and deployment of the frequency multiplexed cryogenic readout electronics for the SPTpol experiment, and concluding with the analysis of data taken by the SPT-SZ instrument. I describe the development of a Bayesian likelihood based method I developed for measuring the integrated Comptonization (Ysz) of galaxy clusters from the Sunyaev-Zeldovich (SZ) effect, and constraining galaxy cluster Ysz-mass scaling relations.
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We describe a method for measuring the integrated Comptonization (YSZ) of clusters of galaxies from measurements of the Sunyaev-Zeldovich (SZ) effect in multiple frequency bands and use this method to characterize a sample of galaxy clusters detected in South Pole Telescope (SPT) data. We test this method on simulated cluster observations and verify that it can accurately recover cluster parameters with negligible bias. In realistic simulations of an SPT-like survey, with realizations of cosmic microwave background anisotropy, point sources, and atmosphere and instrumental noise at typical SPT-SZ survey levels, we find that YSZ is most accurately determined in an aperture comparable to the SPT beam size. We demonstrate the utility of this method to measure YSZ and to constrain mass scaling relations using X-ray mass estimates for a sample of 18 galaxy clusters from the SPT-SZ survey. Measuring YSZ within a 0.75 radius aperture, we find an intrinsic log-normal scatter of 21+/-11% in YSZ at a fixed mass. Measuring YSZ within a 0.3 Mpc projected radius (equivalent to 0.75 at the survey median redshift z = 0.6), we find a scatter of 26+/-9%. Prior to this study, the SPT observable found to have the lowest scatter with mass was cluster detection significance. We demonstrate, from both simulations and SPT observed clusters, that YSZ measured within an aperture comparable to the SPT beam size is equivalent, in terms of scatter with cluster mass, to SPT cluster detection significance.
SPTpol is a dual-frequency polarization-sensitive camera that was deployed on the 10-meter South Pole Telescope in January 2012. SPTpol will measure the polarization anisotropy of the cosmic microwave background (CMB) on angular scales spanning an arcminute to several degrees. The polarization sensitivity of SPTpol will enable a detection of the CMB B-mode polarization from the detection of the gravitational lensing of the CMB by large scale structure, and a detection or improved upper limit on a primordial signal due to inflationary gravity waves. The two measurements can be used to constrain the sum of the neutrino masses and the energy scale of inflation. These science goals can be achieved through the polarization sensitivity of the SPTpol camera and careful control of systematics. The SPTpol camera consists of 768 pixels, each containing two transition-edge sensor (TES) bolometers coupled to orthogonal polarizations, and a total of 1536 bolometers. The pixels are sensitive to light in one of two frequency bands centered at 90 and 150 GHz, with 180 pixels at 90 GHz and 588 pixels at 150 GHz. The SPTpol design has several features designed to control polarization systematics, including: single-moded feedhorns with low cross-polarization, bolometer pairs well-matched to difference atmospheric signals, an improved ground shield design based on far-sidelobe measurements of the SPT, and a small beam to reduce temperature to polarization leakage. We present an overview of the SPTpol instrument design, project status, and science projections.
We present the software system used to control and operate the South Pole Telescope. The South Pole Telescope is a 10-meter millimeter-wavelength telescope designed to measure anisotropies in the cosmic microwave background (CMB) at arcminute angular resolution. In the austral summer of 2011/12, the SPT was equipped with a new polarization-sensitive camera, which consists of 1536 transition-edge sensor bolometers. The bolometers are read out using 36 independent digital frequency multiplexing (dfmux) readout boards, each with its own embedded processors. These autonomous boards control and read out data from the focal plane with on-board software and firmware. An overall control software system running on a separate control computer controls the dfmux boards, the cryostat and all other aspects of telescope operation. This control software collects and monitors data in real-time, and stores the data to disk for transfer to the United States for analysis.
We present Sunyaev-Zeldovich measurements of 15 massive X-ray selected galaxy clusters obtained with the South Pole Telescope. The Sunyaev-Zeldovich (SZ) cluster signals are measured at 150 GHz, and concurrent 220 GHz data are used to reduce astrophysical contamination. Radial profiles are computed using a technique that takes into account the effects of the beams and filtering. In several clusters, significant SZ decrements are detected out to a substantial fraction of the virial radius. The profiles are fit to the beta model and to a generalized NFW pressure profile, and are scaled and stacked to probe their average behavior. We find model parameters that are consistent with previous studies: beta=0.86 and r_core/r_500 = 0.20 for the beta model, and (alpha, beta, gamma, c_500)=(1.0,5.5,0.5,1.0) for the generalized NFW model. Both models fit the SPT data comparably well, and both are consistent with the average SZ profile out to the virial radius. The integrated Compton-y parameter Y_SZ is computed for each cluster using both model-dependent and model-independent techniques, and the results are compared to X-ray estimates of cluster parameters. We find that Y_SZ scales with Y_X and gas mass with low scatter. Since these observables have been found to scale with total mass, our results point to a tight mass-observable relation for the SPT cluster survey.
The BICEP/Keck (BK) experiment aims to detect the imprint of primordial gravitational waves in the Cosmic Microwave Background polarization, which would be direct evidence of the inflation theory. While the tensor-to-scalar ratio has been constrained to be r_0.05 < 0.06 at 95% c.l., further improvements on this upper limit are hindered by polarized Galactic foreground emissions and removal of gravitational lensing polarization. The 30/40 GHz receiver of the BICEP Array (BA) will deploy at the end of 2019 and will constrain the synchrotron foreground with unprecedented accuracy within the BK sky patch. We will show the design of the 30/40 GHz detectors and test results summarizing its performance. The low optical and atmospheric loading at these frequencies requires our TES detectors to have low saturation power in order to be photon-noise dominated. To realize the low thermal conductivity required from a 250 mK base temperature, we developed new bolometer leg designs. We will present the relevant measured detector parameters: G, Tc, Rn, Psat , and spectral bands, and noise spectra. We achieved a per bolometer NEP including all noise components of 2.07E-17 W/sqrt(Hz), including an anticipated photon noise level 1.54E-17 W/sqrt(Hz).
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