Seeing Dark Matter with Weak Gravitational Lensing

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Dark matter (DM) is the dominant form of matter in the Universe, yet it remains poorly understood empirically due to the difficulty in directly measuring its properties. An understanding of DM and its link to visible matter is also critical for disentangling the puzzles of galaxy formation, since DM forms the structural framework of halos and filaments within which the visible parts of galaxies form and evolve. Weak gravitational lensing (WL) has emerged as one of the most promising ways to measure the quantity and spatial distribution of dark matter. The Canada-France Imaging Survey (CFIS) has exceptional power (due to its overlap with the Sloan Digital Sky Survey) for science that combines WL with galaxy spectroscopic redshifts. This combination of WL and spectroscopy is unique in the international context and allows studies of dark matter that no other survey can achieve. I am the Lead Scientist of the r-band (WL) component of CFIS, and lead of the international CFIS WL team. This proposal has two primary scientific objectives. The first objective is to map and characterize the fine details of dark matter structure in haloes and filaments. To meet these goals, my group will use CFIS data to study the dark matter structures in previously unexplored regimes of density or environment: (1) in between galaxies, in the form of filaments of the cosmic web; (2) in tidally stripped halos of satellites (3) the shapes of dark matter haloes and their connection to the large-scale environment. The second objective is to test General Relativity (GR) and the cosmological model on large scales. My group will compare the deflection of light with the infall of galaxies into structures: by combining CFIS WL with SDSS redshift data, we will perform the most stringent test to date. We will measure the relationship between matter and galaxies and gravity on the largest scales and in the nearby Universe through comparisons of large-scale structure and peculiar velocities. WL is the driver behind several billion dollar scale projects (the Euclid satellite, the Large Synoptic Survey Telescope), which promise orders of magnitude increases in lensing power when they begin in the early-to-mid 2020s. The experience gained through CFIS will put my group in an exceptional position to exploit these new surveys in this new golden age of weak gravitational lensing.