Spin alignment around Illustris-TNG voids

Abstract

Using a new statistical approach we study the alignment signal of galactic spins with respect to the center of voids identified in the TNG-300 simulation. We explore this signal in different samples of galaxies, varying their distance from the void center, mass, spin norm, local density, and velocity. We find a strong tendency (>9 sigma) of massive, high-spin, and low radial velocity galaxies to be aligned perpendicularly to the void-centric direction in a wide range of distances corresponding to 0.9 to 1.4 void radii. Furthermore, we find that in these subdense environments, local density is irrelevant in the amplitude of spin alignment, while the largest impact is associated to the galaxy void-centric radial velocity in the sense that those at the lowest expansion rate are more strongly aligned perpendicularly to the center of the void. Our results suggest that further analysis at understanding intrinsic alignments and their relation to large scale structures may probe key for weak lensing studies in upcoming large surveys such as Euclid and LSST.