Speaker
Description
Statistical isotropy is a foundational conjecture in cosmology. However, its validation is a critical task, as theoretical models involving vector fields, such as those in the early universe, naturally lead to its violation. While previous studies using CMB and galaxy clustering have placed constraints on the quadrupolar type of statistical anisotropy (SA), recent N-body simulations have further revealed that SA induces an anisotropic halo bias.
Motivated by these developments, we investigate how SA originating from the early universe affects the distributions of shapes and orientations of cluster-sized halos, using cosmological N-body simulations that incorporate SA. While the three-dimensional halo shape parameters show little dependence on SA, we find that halo orientations are significantly influenced, with halos tending to align either perpendicular or parallel to the SA direction.
This SA-induced alignment becomes more prominent for more massive halos. We also study other vector quantities associated with the dynamics of halos, such as bulk velocity and angular momentum vectors. We find that their dependence on the SA is smaller than that of the orientation vectors. Our findings suggest that observational measurements of projected halo shapes derived from galaxy cluster-galaxy lensing could provide a novel probe of SA in the universe.