Galaxy intrinsic alignments: A new window into structure in the Universe

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Observations of galaxies can be used to map out structure in the Universe and probe some of the greatest mysteries in physics, including “dark matter” and “dark energy.” Upcoming efforts that involve new big telescopes and large collaborations of scientists will observe billions of galaxies. To harness these impressive data sets, it is essential to understand how galaxy properties, especially their shapes, relate to their surrounding environment. Scientists at Northeastern University will use state-of-the-art observations as well as theoretical computer simulations to develop the understanding of galaxy shapes. These advances will enable more accurate studies of the underlying cosmological model, a key goal of the scientific community. Through research opportunities and targeted mentoring, this project will also advance undergraduate training in physics and astronomy, with a particular focus on first-generation, undocumented, and low-income (FUNL) students. Galaxy “intrinsic alignments” (IA) are an important astrophysical effect in which the intrinsic shapes of galaxies are correlated with large-scale structure in the Universe. This effect impacts analyses that involve weak gravitational lensing and galaxy clustering, including planned key studies using data from the upcoming Vera C. Rubin Observatory. IA must be sufficiently well understood to allow tests of the cosmological model that are both accurate and precise. This project will significantly improve the understanding of IA through a coherent program of targeted observations and novel, efficient simulation techniques. Using the final data set of the Dark Energy Survey, the team will employ several strategies designed to probe IA in different regimes, unified through a single analysis framework. Informed by these measurements, simulated galaxies with realistic IA will be produced from gravity-only simulations, avoiding the computational challenges of hydrodynamic simulations, and allowing the production of mock galaxy catalogs in large cosmological volumes and with a wide range of IA properties. The insights from these efforts will enable a substantial improvement in the ability to mitigate IA in future analyses. In addition, the team will use their results and simulation capabilities to develop IA as a probe of astrophysics and cosmology with next-generation data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.