Astrophysics and Cosmology with Line Intensity Mapping

Line Intensity Mapping (LIM) is a rapidly emerging technique which promises new insights into the evolution of the universe across cosmic history. By measuring the integrated emission of spectral lines over a broad range of frequencies one can observe the statistical properties of distant galaxies. LIM surveys have depth and resolution requirements that are greatly relaxed compared to direct- imaging surveys. A coordinated, comprehensive, multi-line intensity mapping effort can efficiently probe over 80% of the volume of the universe while retaining the redshift resolution necessary to make three-dimensional maps - a feat beyond the reach of other methods. Such measurements can uniquely address a wide range of pressing mysteries in galaxy evolution, cosmology, and fundamental physics. Among them are the history of star formation, the process of reionization, cosmological inflation, the validity of general relativity, and the nature of dark matter and dark energy. Several LIM efforts are already well underway, a number of which with significant Canadian involvement. Surveys targeting the 21 cm line have been active for some time, including the Canadian- led CHIME experiment. Recently, experiments targeting other atomic and molecular lines across the electromagnetic spectrum have garnered significant interest as well. Such observations have useful synergies with each other,and are highly complementary to astrophysical measurements from other surveys that Canada is a key participant in. With continued investment over the next decade, LIM experiments will have a transformative impact on our understanding of the distant universe. However, significant modeling, analysis, and interpretation challenges remain in these measurements. We therefore motivate a broad-based program of line intensity mapping theoretical, simulation, and observational efforts to ensure that intensity mapping techniques reach their full potential.White paper identifier W03