Cosmic Microwave Background and Large Scale Structure: Cross-Correlation as seen from Herschel and Planck satellites

As well as providing us with a snapshot of the Universe at the time of recombination, the cosmic microwave backround (CMB) radiation carries a wealth of information about the later evolution of the Universe through the so-called CMB secondary anisotropies that originates from the interaction between CMB photons and the Large Scale Structure (LSS). This thesis deals with two of these effects: the CMB lensing and the kinematic Sunyaev-Zel'dovich (kSZ). In particular, we present the first cross-correlation analysis between the CMB lensing maps reconstructed by Planck team and the angular position of galaxies from the Herschel H-ATLAS survey, the highest redshift sample exploited for cross-correlation analysis to date. By splitting the galaxy catalog in two redshift bins, we also attempt a tomographic analysis of the signal and reconstruct the galaxy bias evolution over cosmic time. On the other hand, the kSZ effect measures the integrated free electron momentum up to high redshift, thus being sensitive to the cosmic flows and the reionization history. Here we study its capabilities in constraining theories of modified gravity

Searching for the Cosmic Dawn with the Hyperfine Structure Transition of Hydrogen

The 21 cm hyperfine structure transition of neutral hydrogen promises to open a window into the first billion years of the Universe (z &#62; 6). With the exception of rare lines of sight towards exceptionally distant and luminous galaxies, this period of the universe's history remains largely unexplored. During this time the 21 cm transition is expected to be detectable as a 10--100 mK perturbation in the thermal Cosmic Microwave Background (CMB) spectrum. Due to the large field of view of low frequency radio telescopes (typically composed of dipole antennas) and the fact that the line of sight distance can be inferred from the measured frequency of the transition, the ultimate goal of 21 cm cosmology is to produce three dimensional tomographic maps of the 21 cm brightness temperature. In this way, the formation of the first stars and galaxies will be revealed through their influence on the neutral gas around them. This thesis saw the construction of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), a new low frequency (27--85 MHz) radio telescope located near Bishop, California. Composed of 288 crossed-dipole antennas, the OVRO-LWA is capable of imaging the entire visible hemisphere in a single 13 s snapshot image with 8 arcmin angular resolution. The primary challenges faced by efforts to detect the highly redshifted 21 cm transition are seeing past the blinding glow of foreground radio emission that is five orders of magnitude brighter than the cosmological emission, and calibrating the instrument to a level where it's possible to make the separation between foreground emission and the 21 cm signal. In this thesis I will present foundational work using the OVRO-LWA to place upper limits on spatial fluctuations of the 21 cm transition during the Cosmic Dawn---the period of first star formation. In this thesis I present the highest angular resolution maps of the full sky below 100 MHz, and generated with a new widefield imaging technique that is specialized for drift scanning interferometers. These sky maps are a 10-fold improvement in angular resolution over existing maps at comparable frequencies, and are publicly available now for use in modeling and subtracting the contamination of foreground emission in 21 cm experiments. Using a 28 hr integration with the OVRO-LWA, I place to-date the most constraining upper limits on the amplitude of the 21 cm spatial power spectrum at the Cosmic Dawn, and the first limits at z &#62; 18. Although the current constraints Δ212 ≲ (104mK)2 do not meaningfully restrict the parameter space of models of early star formation, they do inform the design and calibrations necessary for future measurements to push towards a detection of the high-redshift 21 cm transition. In making this measurement I demonstrate the application of a new foreground filter that accounts for the full covariance of the foreground emission, and provide an updated measurement of the foreground angular covariance. Finally, I interpret the limiting factors in this measurement and determine the instrumental calibration and characterization requirements the OVRO-LWA will need to achieve in order to make a detection of the 21 cm power spectrum of the Cosmic Dawn.</p

Spatial and Time Clustering of the High-Energy Photons collected by the Fermi LAT

The past decade has seen a dramatic improvement in the quality of data available at both high (HE, > 10 GeV ) and very high (VHE, > 100 GeV ) gamma-ray energies. Thanks to the latest Pass8 data release by Fermi LAT which increases the overlap in energy coverage with Cherenkov Telescopes, we can extend the observation in gamma rays until few TeV. We developed, applied and tested a new time and spatial clustering algorithm, which is able to analyse the whole Fermi LAT data set (about 7 years) as well as sets of shorter time intervals. Using time and spatial clusters of HE photons collected by the Fermi LAT data we both provide new candidates for VHE experiments and study the variability of gamma-ray properties of known HE sources.ope

Calibration Instrumentation for the Hydrogen Intensity and Real-Time Analysis eXperiment

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a 21 cm neutral hydrogen intensity mapping experiment to be deployed in the Karoo Desert in South Africa. It aims to improve constraints on the dark energy equation of state through measurements of large-scale structure at high redshift, while doubling as a state-of-the-art fast radio burst (FRB) detector. This dissertation focuses on two aspects of the HIRAX instrument characterization: (1) optimizing the signal-to-noise of antennas, through the design and implementation of a custom test-bed for determining the noise temperature of radio antennas operating between 400-800MHz, and (2) mapping the HIRAX telescope beam pattern with a custom drone calibration system. The work described is critical to HIRAX\u27s development, both by informing final antenna design and providing the tools to generate beam maps that will factor into all cosmological analysis