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Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xv,110 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Robert J. Scherrer, Dept. of Physics. Includes bibliographical references (p. 106-110).

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This thesis presents the measurement of the cosmic microwave background (CMB) power spectrum for the Atacama Cosmology Telescope (ACT) experiment and its polarized upgrade, ACTPol. I present the tools that I have developed for constructing unbiased and nearly optimal statistical estimators. I discuss how to separate the cosmological and the astrophysical signal and how to characterize instrumental systematics. The goal of this work is to obtain accurate power spectra measurement that can be used for cosmological parameter estimation. I first present the analysis of the complete ACT data set. The high resolution of the telescope allows us to recover power spectra to ℓ = 10000. I report the measurement of the power spectra at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. The power spectrum measurement is consistent with the ΛCDM model and a basic foreground model. I then present the cross correlation of maps from the Atacama Cosmology Telescope with maps from the Planck satellite in two overlapping regions covering 592 square degrees. I find excel- lent agreement between the two datasets at both frequencies, quantified using the variance of the residuals between the ACT power spectra and the ACT×Planck cross-spectra. The next generation of CMB experiments are focused on measuring its polarization. I present efficient algorithms for CMB lensing simulation and power spectrum estimation for flat-sky CMB polarization maps. Finally, I discuss the first temperature and polarization power spectra measurement from the ACTPol experiment. They are the first attempt to measure the polarization of the CMB at high resolution.

Simulations and observations of the microwave sky are of great importance for under- standing the Universe that we reside in. Specifically, knowledge of the Cosmic Microwave Background (CMB) and its foregrounds – including the Sunyaev-Zel’dovich (SZ) effect from clusters of galaxies and radio point sources – tell us about the Universe on its very largest scales, and also what the Universe is made of. We describe the creation of software to carry out large numbers of virtual sky simulations. The simulations include the CMB, SZ effect and point sources, and are designed to examine the effects of point sources and the SZ effect on present and recent observations of the CMB. Utilizing sets of 1,000 simulations, we find that the power spectrum resulting from the SZ effect is expected to have a larger standard deviation by a factor of 3 than would be expected from purely Gaussian realizations. It also has a distribution that is significantly skewed towards increased values for the power spectrum, especially when small map sizes are used. The effects of the clustering of galaxy clusters, residual point sources and uncertainties in the gas physics are also investigated, as are the implications for the excess power measured in the CMB power spectrum by the CBI and BIMA experiments. We also investigate the possibility of using the One Centimetre Receiver Array (OCRA) receivers to observe the CMB and measure this high-multipole excess. An automated data reduction package has been created for the OCRA receivers, which has been used in end-to-end simulations for OCRA-p observations of point sources. We find that these simulations are able to realistically simulate the noise present in real observations, and that the introduction of 1/ f noise into the simulations significantly reduces the predicted ability of the instruments to observe weak sources by measuring the sources for long periods of time. The OCRA-p receiver has been used to observe point sources in the Very Small Array fields so that they can be subtracted from observations of the CMB power spectrumWe find that these point sources are split between steep and flat spectrum sources. We have also observed 550 CRATES flat spectrum radio sources, which will be useful for comparison to Planck satellite observations. Finally, the assembly and commissioning of the OCRA-F receiver is outlined. This receiver is now installed on the Torun ́ 32-m telescope, and is currently being calibrated prior to starting observations in the next few months.

In this thesis I construct various models to interpret measurements of the clustering of dusty star-forming galaxies through the angular power spectrum statistic. The goals of this work are, firstly, to facilitate the separation of the dusty galaxy contribution from the cosmic microwave background background (CMB) power spectrum, and, secondly, to improve our understanding of the physical properties of these galaxies. I present analysis of the first cross-correlation of millimeter and submillimeter sky maps, using data from the Atacama Cosmology Telescope (ACT) and the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST), which revealed that the dusty galaxies that dominate the submillimeter sky are, to a significant extent, those same sources that are a nuisance contaminant for CMB cosmology. I then perform a joint fit to the ACT and BLAST power spectra as well as early results from the Planck Surveyor to construct a simple phenomenological template for the frequency and angular scale dependence of the contribution from clustered dusty galaxies to the total power spectrum. This template may be used to assist in extracting the CMB signal from future ACT and other data sets. The correlation between dusty galaxies and the thermal Sunyaev Zel'dovich effect leads to an additional contribution to the measured angular power spectrum that further hampers constraining quantities of cosmological interest. I present the first physically-motivated model for this correlation, and make predictions for its frequency and scale dependence as a CMB foreground. Finally, I combine angular power spectrum measurements from ACT, Planck and other instruments with deep far-infrared and submillimeter source number counts and constrain a model for the emission properties of these dusty galaxies. I demonstrate that the power spectrum carries significant constraining power and can improve our understanding of dust emission and star formation from unresolved objects at high redshift.

In this thesis, I present my work related to the characterization of diffuse Galactic foregrounds for observing the polarization of the Cosmic Microwave Background (CMB) radiation, and the impact of these foregrounds on the measurement of cosmological parameters. One of the most important future challenges for cosmology is the potential detection of polarization B-modes of the CMB. Inflation is a theory that explains the extremely early Universe, and solves several problems that were present in classical cosmology. It describes the anisotropies observed in the current Universe as primordial quantum fluctuations stretched by rapid exponential expansion. A key prediction of inflation is the production of a background of primordial gravitational waves, which could be detected through the associated large-scale B-mode signal in the CMB polarization. The amplitude of the B-mode signal, which depends on the energy scale of inflation, is parametrized by the tensor-to-scalar ratio r. Diffuse emission from within our Galaxy, and other extra-Galactic sources, collectively referred to as CMB foregrounds, obscure a fraction of the cosmological signal from the CMB radiation. This is a huge problem, because they have to be cleaned using data analysis methods, called component separation. A significant challenge for the potential detection of the primordial B-mode signal is that it can be extremely small, to the extent that it can be dominated even by the residual foreground contamination after component separation. In this work, we characterize these foreground residuals and assess their impact on the cosmological parameters. We create a method to simulate observations of the microwave sky, including diffuse Galactic foregrounds, CMB realizations and instrumental noise. These simulations are used to propagate errors on the characterization of foregrounds through the analysis procedures employed in the observations of the CMB, including component separation, angular power spectra calculation and cosmological parameter estimation. We estimate the bias and the σ error for the tensor-to-scalar ratio, to quantify the impact of the foreground residuals in the cosmological signal. We also propose a novel method to model these residuals when determining cosmological parameters, in order to avoid a bias on the r parameter. We performed forecasts and optimization analyses for two proposed CMB polarization experiments: the Simon Observatory, a funded ground-based telescope that will observe the polarization of the CMB from the Atacama desert in Chile, and CORE, a proposed next-generation CMB satellite experiment. All of our work shows that the issue of foreground residuals must be considered very carefully in future studies. Foreground spectral parameters must be modelled very accurately, with errors < 0.5%, if we wish to measure a value r âˆ1⁄4 10^−3. These foreground residuals can easily be mistaken as primordial cosmological signals, so our work motivates further research into developing new data analysis techniques.

The inflationary paradigm has become widely accepted as an accurate framework in which to describe the physics of the early universe, due both to the conceptual advantages of the idea and the agreement of its predictions with observational data. However, it remains to be determined which of the many detailed theories of inflation correctly describe the universe in which we live. Any such theory faces the challenge of making accurate predictions which agree with observation while also fitting consistently into a theory of high energy physics. Within this challenge there exists the great opportunity to constrain speculative models of fundamental physics. Inflation thereby provides an observational window into theories conventionally thought to be unreachable by experiment. Measurements of anisotropies in the cosmic microwave background radiation and the distribution of large scale structure have proved to be invaluable tools to probe inflation. There has been recent interest in examining the deviations from gaussianity in the statistics of the observed fluctuations. These higher order statistics, if conclusively discovered, stand to teach us a great deal about inflation. Forthcoming data including improved measurements of the cosmic microwave background temperature and polarization will provide additional means to investigate the inflationary era. It is important to understand precisely what impact inflation has had on the universe we observe and thus understand precisely what observation can tell us about inflation and how it may fit into a fundamental theory of physics. We will show the conditions under which the cosmological correlation functions generated during inflation are conserved, and thus identify the conditions which allow us to use observations today to learn about inflation. We first prove a general result which applies only to the leading approximation of the correlation functions, and then we discuss how to treat the additional complications that come with subleading corrections. Next, we will discuss the observational implications of achieving the conditions for conservation for a particular class of inflationary models. Lastly, we discuss one example of how observations can be used to probe non-inflationary physics beyond the standard cosmological model. / text