Forecasting High-z Galaxy-Cosmic Web Alignments for Subaru-PFS

Galaxy formation theory predicts that the shapes of elliptical galaxies and the spins of spiral galaxies are aligned to matter inflows in the cosmic web. This leads to intrinsic alignments between galaxies, which are important to quantify for weak lensing surveys. When attempting to measure galaxy-web alignment at z ~ 2, the paucity of observable galaxies means that only Lyman-alpha tomography is able to reconstruct the cosmic web at a sufficient resolution. We use a ~0.51 deg² mock lightcone extracted from the Bolshoi-Planck dark matter-only cosmological simulation to show that a robust galaxy shape-cosmic web alignment trend exists in 3D real space and redshift space. This trend is well-preserved when the cosmic web is reconstructed from a mock Lyman-alpha tomography survey with parameters equal to the current CLAMATO and upcoming Subaru-PFS surveys, and remains significant when the galaxies are projected onto the sky. We estimate the extent to which an alignment signal can be detected for the upcoming Subaru-PFS survey, for the survey’s redshift targets at z ~ 1.2 and z ~ 2.4. Finally, in preparation for future work constraining an alignment signal in the CLAMATO survey, we extend an existing analytic model for generating galaxy shapes/spins from alignment signal parameters, and show that it is able to accurately capture both shape and spin galaxy-web alignment signals.