Gary Hinshaw


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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

A detection of cosmological 21 cm emission from CHIME in cross-correlation with the eBOSS Lyman-?? forest (2023)

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio telescope that we built to map the large-scale structure of the Universe between redshifts 0.8 and 2.5, when dark energy is expected to begin the transition from a decelerating to an accelerating phase in the expansion of the Universe. CHIME was designed to perform an intensity mapping survey using the 21 cm line of neutral hydrogen, a novel method that has the potential to enable enormous surveys of the distant Universe, but also significant observational challenges to overcome. In this thesis, I describe contributions I made to the CHIME data acquisition system and calibration effort, culminating in a detection of cosmological 21 cm emission in cross-correlation with measurements of the Lyman-? forest. The large data rate from the CHIME correlator is processed in real time by a high-performance digital pipeline, the development of which I participated in extensively. A few specific processing tasks where I led the design and implementation are highlighted in this work. In order to detect the 21 cm signal amidst the much brighter foreground emission from nearby sources, a very precise instrumental calibration is required. Calibrating the telescope's beam is a particular concern. One of many approaches being pursued for CHIME is the holographic observation of bright celestial sources in concert with a second radio telescope. I describe work I did to derive beam measurements from such observations and their analysis, including a scheme for calibrating the polarised beam response. I report the detection of 21 cm emission at an average redshift z = 2.3 in the cross-correlation of CHIME maps with measurements of the Lyman-? forest from the eBOSS. Data collected by CHIME over 88 days in the 400-500 MHz frequency band (1.8
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Calibration and cross-correlation with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) (2022)

Hydrogen intensity mapping is a new technique to map the three-dimensional distribution of matter in the universe. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is at the forefront of the development of intensity mapping and will produce the largest survey of the universe ever done. This dissertation describes my contributions to the calibration and analysis of CHIME data.The two types of amplifiers used in the telescope were characterized for their thermal complex gain susceptibility. In addition, a system of thermometers for the low-noise amplifiers was developed and deployed. The data is presented and its usefulness assessed.A thermal model for the amplitude of the telescope gains was developed based on gains extracted daily from bright point source transits. The model is effective in reducing the common-mode per-input variability (standard deviation) of the gains amplitude from 1.5% to 0.75% at the high end of the frequency band. The effect is smaller at the lower end of the band where the instrument thermal susceptibility is smaller. The model was tested by beam-forming on visibility data and the possibility of expansion of the model was assessed via singular value decomposition of the gains data.A program to cross-correlate the CHIME data with the Sloan quasar catalog was developed. This is done via a frequency stack on frequency-shifted beam-formed CHIME data. The existing codebase for sky simulations was expanded to allow for correlated tracers with different biases using the Zeldovich approximation. The analysis pipeline was expanded to allow for the generation of selection function-aware mock quasar catalogs, for the beam-forming of visibility data on arbitrary positions and for the frequency shifting and stacking of formed-beam spectra.A 13-σ detection of the cross-correlation signal was obtained. The detected signal shows a 4.6-σ deviation from zero frequency lag which might indicate a systematic difference between the redshift inferred from quasar emission lines relative to the redshifts of their host galaxies. The foreground filtering transfer function is estimated from simulations and used to estimate the un-filtered brightness of the HI-quasar cross-correlation signal at 68.6±5.4 μJy/beam.

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The effects of calibration errors and foreground filters on the CHIME power spectrum measurement: a study with simulations and real data (2022)

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift-scan radio telescope designed to map large-scale structure in the universe using the redshifted 21 cm line emitted by neutral hydrogen. By observing the 400 MHz to 800 MHz frequency band, CHIME will measure the expansion rate of the universe in the redshift range z = 0.8 – 2.5 to constrain the nature of dark energy. In this frequency range, astrophysical foregrounds from the Galaxy and extragalactic point sources are much brighter than the 21 cm emission. This requires aggressive foreground filtering. We developed a new implementation of the Karhunen-Loeve transform that correctly tracks the signal and noise power in our data to enable us to filter bright foregrounds. Moreover, we significantly improved the foreground model by modelling the point source sky component based on source count models for both the clustered and Poisson distributed sources with a parameterized maximum flux density cut for point sources which have not been explicitly subtracted from the data. The data volumes for CHIME are extremely large, therefore we developed an upgraded parallelized power spectrum estimation pipeline which is able to forecast the Fisher information matrix and estimate power spectra for three times the frequency range and five times the number of unique baselines by distributing the power spectrum bands across nodes. This allows us to scale the Monte-Carlo simulations to arrays almost as large as CHIME. Due to the bright astrophysical foregrounds CHIME has very stringent calibration requirements. We wrote an end-to-end simulation pipeline and studied various realistic sources of calibration uncertainties with it. The calibration requirements are very stringent and CHIME currently does not quite meet the requirements when using the Karhunen-Loeve foreground filter. We investigated different processing choices on power spectrum estimation with CHIME data in the 610 MHz to 680 MHz band with a selection of short baselines to ensure quick computation times. Even with our currently best calibration procedures our power spectrum estimates are several orders of magnitude higher than the expected from the 21 cm signal. Using a delay filter as an intermediate processing step reduces the power further.

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Probing the universe with multiple large-scale structure tracers (2021)

Different large-scale structure(LSS) tracers bear rich information about our Universe. In this dissertation, I present my studies on galaxy clusters and multi-tracer cross-correlations to highlight the potential and importance of combining multiple LSS tracers in studying our Universe. I use simulated clusters from the BAHAMAS simulation to study the off-centring effect. I define seven observational-motivated centroids from stars, as well as X-ray and thermal Sunyaev-Zeldovich (tSZ) effect data of these clusters. I find that stacked, mis-centred density profiles yield highly biased shape and size parameters. I also quantify and model the offset distributions between these centroids and the `true' centre of these clusters. The fitting is useful for future measurements of stacked density profiles.With the same set of simulated clusters, I evaluate the ability of Convolutional Neural Networks (CNNs) to measure galaxy cluster masses from cluster images. I independently train four separate networks with images of the four tracers mentioned above. I also train a `multi-channel' CNN that predicts mass from all these four tracers. For the clusters that have masses in the range $10^{13.25}\mathrm{M}_{\odot}
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Probing the Large-Scale Structure of the Universe with the Sunyaev-Zel'dovich Effect (2017)

The Sunyaev-Zeldovich (SZ) effect is a spectral distortion in the Cosmic Microwave Background (CMB), due to up-scattering of CMB photons by high energy electrons in clusters of galaxies or any cosmic structure. The Planck satellite mission has measured the spectral distortion with great sensitivity and has produced a full-sky SZ (y) map, which can be used to trace the large-scale structure of the Universe.In this dissertation, I construct the average SZ (y) profile of ∼ 65,000 Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey Data Release 7 (SDSS/DR7) using the Planck y map and compare the measured profile with predictions from the cosmo-OWLS suite of cosmological hydrodynamical simulations. This comparison agrees well for models that include feedback from active galactic nuclei (AGN feedback).In addition, I search for the SZ signal due to gas filaments between ∼260,000 pairs of LRGs taken from the Sloan Digital Sky Survey Data Release 12 (SDSS/DR12), lying between 6-10 h −1 Mpc of each other in the tangential direction and within 6h −1 Mpc in the radial direction. I find a statistically significant SZ signal between the LRG pairs. This is the first detection of gas plausibly located in filaments, expected to exist in the large-scale structure of the universe. I compare this result with the BAHAMAS suite of cosmological hydrodynamical simulations and find that it predicts a slightly lower, but marginally consistent result.As an extension of my MSc. thesis work, I study CMB polarization. The B-mode component of CMB polarization is an important observable to test the theory of inflation in the early universe. However, foreground emissions in our own galaxy dominates the B-mode signal and therefore multi-frequency observations will be required to separate any CMB signal from the foreground emission. I assess the value of adding a new low-frequency channel at 10 GHz for the foreground removal problem by simulating realistic experimental data. I find that such a channel can greatly improve our determination of the synchrotron component which, in turn, significantly improves the reliability of the CMB separation.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Utilities for the Canadian galactic emission mapper (2023)

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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E-B decomposition of CMB polarization using deep learning (2022)

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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Finding constraints on dark energy using hydrogen intensity mapping (2018)

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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Towards precision measurements of the Hubble constant with the Canadian Hydrogen Intensity Mapping Experiment (2018)

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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Probe the universe with PIXIE experiment and tSZ-lensing cross-correlation (2017)

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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A Study of Radio Frequency Interference for the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder (2014)

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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10GHz sky survey to probe inflation with CMB polarization (2013)

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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