Gary Hinshaw

The Cosmic Microwave Background (CMB) has proven to be a scientific gold mine in the field of cosmology over the past 50 years. It’s blackbody spectrum and anisotropy measurements have enabled the determination of the main cosmological parameters under the Λ-Cold Dark Matter (ΛCDM) model. In the recent years, scientists have switched their interest towards the study of the CMB polarization field. The inflationary model, which aims to explain the very early universe predicts a period of exponential expansion when the universe was only 10ˉ³⁴ seconds old. This rapid expansion is theorized to have produced primordial gravitational waves (PGW) that could have survived long enough to leave an imprint in the polarization field of the CMB, in the form of B−modes. Among the several challenges in the search for this cosmological signal, the presence of foregrounds between us and the CMB is one of the most difficult to overcome. The synchrotron radiation from our galaxy dominates over the faint polarized emission from the CMB in its observing frequency, ∼ 100 GHz. The Canadian Galactic Emission Mapper (CGEM) is a planned four metre, single dish radio telescope that will map the Northern sky in polarization in the 8-10 GHz range. By measuring in this frequency window, it will produce the most precise large-area polarization maps ever made in a window where the galactic signal is ∼ 10³ times higher than in the CMB frequency range. These maps will be subsequently used by B−modes search experiments to improve their foreground models. CGEM will be extremely relevant for CMB polarization science. A secondary goal is a better understanding of the interstellar medium in our galaxy. This thesis describes my contributions to making CGEM happen. We present a simulation pipeline developed and tested to inform the design of the telescope and to simulate time ordered data. We also show part of the design, development and testing of the radiometer that will go into CGEM.

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The polarization of the cosmic microwave background (CMB) can be split into two coordinate independent components: the gradient-like E-mode, and the curl-like B-mode. Primordial B-modes are of particular interest as they do not arise from scalar density perturbations and serve as a direct probe of primordial gravitational waves theorized to be generated during inflation. A direct detection of these elusive B-modes would help determine the energy scale of inflation and constrain possible inflationary models.However, the E-B decomposition of polarization on a partial or cut sky is non-unique and introduces modes that cannot conclusively be classified as pure E or B. This is a source of ambiguity for all CMB experiments probing polarization as a Galactic cut is required even for purported full-sky missions, such as the European Space Agency’s (ESA) Planck mission. We present a map-based technique using machine learning (ML) methods to perform this partial sky decomposition.In particular, we use a deep residual convolutional neural network (CNN) based on the U-Net architecture to perform this decomposition on small patches of the sky 400 square degrees in area, allowing the targeting of regions with low Galactic foreground. Our deep residual U-Net performs exceptionally well at angular scales of a few degrees, corresponding to spherical harmonic Fourier modes l (ell) ≃ 50 to 110, a range of scales ideal for probing the recombination bump of the primordial B-mode power spectrum. Additionally, the map-based nature of our technique allows visual inspection of the E-B separation. This may be especially useful for identifying residual Galactic contamination in polarization data.

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In this MS.c. thesis, we demonstrate a method for estimating the expansion history of the universe using the hydrogen intensity map from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which will be generated in the near future. This map will be in angular and redshift space, where redshift of the hydrogen due to the expansion serves as a time variable. The expansion history, dependent on cosmological parameters via the Einstein equations, determines the distance away from us in units of a grid comoving with the expansion at which light of each redshift was emitted. We use knowledge of the fixed comoving distance, approximately 150 megaparsecs, that baryon acoustic oscillations, or primordial sound waves, traveled away from the centers of matter perturbations, where there is a corresponding peak in the matter correlation function subject to uncertainty of the initial quantum mechanical fluctuations. We explain the method by which we fit the correlation function to a model for expansion determined by the equation of state of dark energy, to constrain this parameter. We test the method using a three-dimensional realization of the theoretical matter power spectrum calculated from CAMB (Code for Anisotropies in the Microwave Background), providing an estimate of constraints obtained from a small redshift region spanning one sound horizon diameter in redshift space assuming a constant equation of state of dark energy and fixed values of the other cosmological parameters. We explain how to generalize this method to a more complete analysis.

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The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer located at the Dominion Radio Astrophysical Observatory in Penticton, BC. It is designed to map large- scale structure in the universe by observing 21 cm emission from the hyperfine transition of neutral hydrogen between redshifts 0.8 and 2.5. CHIME will perform the largest volume survey of the universe yet attempted and will characterize the BAO scale and expansion history of the universe with unprecedented precision in this redshift range. CHIME achieved first light in the fall of 2017 and instrument commissioning is underway. In this work I present sensitivity forecasts and derive constraints on cosmological parameters given CHIME’s nominal survey. The broad redshift range of the observations will enable tight constraints to be placed on the Hubble constant H0 , independent of CMB or local recession velocity measurements. Precision measurements of this epoch will shed new light on the tension between direct measurements of the Hubble constant vs. those inferred from high-redshift observations, notably the CMB anisotropy. CHIME measurements together with a prior on the baryon density from measurements of deuterium abundance are enough to place constraints on H0 at the 0.5% level assuming a flat ΛCDM model, with uncertainty increasing to ∼ 1% if curvature is allowed to vary, or up to ∼ 3% for a dark energy equation of state with w/= −1. Including priors from CMB measurements, in the scenario where the datasets are consistent, narrows these uncertainties further, most significantly in the model where w is a free parameter.

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The polarization of Cosmic Microwave Background can help us probe theearly universe. The polarization pattern can be classified into E-mode and B-mode. The B-mode polarization is a smoking gun of cosmological inflation.PIXIE is an in-proposal space telescope observing CMB polarization. Itis extremely powerful to extract CMB polarization signal from foregroundcontamination. The second chapter of this thesis summarizes my work onoptimizing the optical system of PIXIE. I run a Monte-Carlo Markov Chainfor the instrument parameters to maximize the value ”Good” which judgesthe behavior of the instrument. For the optimized instrument, with all kindsof noises from inside instrument and wrong polarization taken into account,good rays from the sky make up of 15.27% of all the rays received by thedetector. The instrument has a 1.1° top-hat beam response.The third chapter summarizes my work on studying the potential con-tamination in the reconstructed y map by doing cross-correlation betweentSZ signal and weak lensing. The weak lensing data is the convergence mapfrom the Red Sequence Cluster Lensing Survey. I reconstruct the tSZ mapwith a Needlet Internal Linear Combination method with 6 HFI sky mapsmade by Planck satellite. The reconstructed cross correlation is consistentwith Planck NILC SZ map. I take Cosmic Infrared Background (CIB) andgalactic dust as two potential source of contamination in the reconstructedmap. I find that κ × CIB contributes (5.8 ± 4.6)% in my reconstructed NILCy map for 500
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The following document describes pursued studies to understand the properties of radio frequency interference (RFI) which affects the quality of the data of the Canadian Hydrogen Intensity Mapping Experiment Pathfinder at the Dominion Radio Astronomy Observatory in Penticton, British Columbia. The Canadian Hydrogen Intensity Mapping Experiment is a challenging project aimed to trace large scale structure by observing the 21cm emission line of neutral hydrogen in the frequency spectrum 400-800MHz to research the nature of Dark Energy.RFI is terrestrial signal caused by radio bands, TV stations, satellites etc. that produces unwanted disturbances in the frequency spectrum which adds power to the data. It represents a challenge to measure faint sources in the sky and we seek ways to identify it based on its statistical properties such as non-Gaussianity.We have designed algorithms that aim to identify and flag RFI in our data. Digital TV bands cause permanent corruption in the affected frequency bins and account for a 19% loss of bandwidth.The 5 sigma threshold cut searches for time-varying RFI in each frequency bin. Outliers above 5 standard deviations are iteratively flagged but not all of the occurring RFI were recognized due to non-Gaussianity.The median absolute deviation cut is a robust statistical method that uses sky data only. Identification of short-lived and long-lived RFI occurrences originating mainly from the sky has been successful.A correlation coefficient algorithm uses a combination of a reference RFI antenna sensitive to the horizon and a sky antenna to find correlated signals that are significantly above expected thermal noise of the radiometer while disregarding correlation due to sky signal. RFI at the horizon is well recognized by this method.

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The fluctuations in the cosmic microwave background(CMB) contain a lot of information on the history and composition of our universe. In particular, the rich detail about our early universe is included in the angular power spectra of the CMB fluctuations, which constrains the cosmological parameters in current models of the universe. The latest cosmological data strongly support an inflationary Lambda CDM cosmology with a minimal six parameters to describe our universe. The next challenge in cosmology is to probe the physics of the inflationary period by looking for the signature of primordial gravitational waves in the polarized CMB. CMB polarization was generated at last scattering by scalar and tensor perturbations in the primordial fluid. The tensor perturbations are produced by the stretching of space-time by gravitational wave fluctuations, while scalar perturbations are produced by density fluctuations in the primordial fluid. The ratio of the tensor to scalar perturbation amplitude, r, is a key tracer of the physics of the inflationary epoch, which is deeply connected to the energy scale of inflation in a standard inflationary model. A local quadrupole anisotropy in the radiation field at the time of decoupling causes the linear polarization in CMB through Thomson scattering by electrons. The CMB polarization can be decomposed into two rotationally invariant quantities, called E and B. The CMB B-mode is a direct tracer of the tensor perturbations caused by gravitational waves in the inflationary period of the universe. Thus, the detection of B-mode has currently been dubbed the ''smoking gun'' of inflation. However, the galactic foreground emissions also have much stronger E- and B-modes polarization. We intend to produce half-sky maps of total intensity and linear polarization at 10 GHz. This data would probe galactic synchrotron emission and also can help constrain the so-called anomalous emission. Therefore, the maps can be used with other surveys such as WMAP and Planck to subtract galactic foreground emissions and obtain more precise CMB data. In addition, the data will give us information about galactic emission components such as synchrotron, free-free, thermal dust and anomalous emission in the microwave range.

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