Martin, Hunter2026-03-232026-03-232026-03-232026-03-23https://hdl.handle.net/10012/22978The field of cosmology is currently in an era principally focused on statistical precision. To achieve greater precision, deeper and wider surveys are actively being developed and conducted to gather more and more information about the surrounding cosmos. Alternatively, there are efforts to develop new statistical probes to better utilize currently-existing data to obtain tighter constraints. Cosmic voids, as vast underdense regions, then represent an ideal candidate to complement the statistical information already extracted from the opposite density extremes: massive luminous galaxies and galaxy clusters. Voids have already seen some success in constraining cosmology through probes like the void size function and void-galaxy cross-correlations. This thesis introduces the matter distribution within cosmic voids as measured by weak gravitational lensing as a new probe that is significantly detectable within current and future data sets. The goal of this demonstration is to justify future efforts in extracting the cosmological information from this newfound signal. For data currently available, we make use of the large overlap of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) and the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). We measure void lensing around BOSS voids and find that we can detect the signal at 6.2 sigma significance, the most significant detection from spectroscopically-identified voids to date. We additionally are able to significantly detect differences in the void profile with void size between the larger half and smaller half of the void catalogue at 2.3 sigma. To help perform this measurement, we present and validate a novel method for computing the Gaussian component of the conventional weak lensing covariance, adapted for use with void studies. Comparing the void profile to a measurement of the void-galaxy cross-correlation to test the linearity of the relationship between mass and light, we find good visual agreement between the two, and a galaxy bias factor of 2.45 pm 0.36, consistent with other works. We additionally assist in future developments of the UNIONS data by running quality control tests for the future photometric redshift data sets. These future releases will provide additional data to make these detections stronger. For future data, we use the Flagship simulation of the Euclid survey to simulate the expected data from the Euclid VISible imager (VIS) and Near-Infrared Spectrometer and Photometer (NISP) instruments across an octant of the sky. This octant then roughly corresponds to an equivalent area of the planned second data release of the survey. We extend the methodology and covariance model to a lensing tomography setup by binning voids and sources along the line of sight. We then stack information along source bins. From this, we are able to detect the void lensing profiles with 12 sigma, 11 sigma, 7.1 sigma, and 4.7 sigma significance across the four different void redshift bins. Scaling the most significant result to the expected areas for the first and final data releases, we get 6.9 sigma and 21 sigma respectively. We additionally find a 4.4 sigma difference between the lensing profiles of the smallest voids and the largest voids.enweak gravitational lensinglarge scale structuredark mattercosmologyDoctoral Thesis