On the Environmental Dependence of Galaxy Properties Established by the Initial Cosmological Conditions

Abstract

We study theoretically how the initial cosmological conditions establish the dependence of galaxy properties on the environment. First, we adopt the linear tidal torque theory according to which the angular momentum of a proto-galaxy is generated at first order by the misalignment between the proto-galaxy inertia tensor and the local tidal tensor. Then, we quantify analytically the degree of the misalignment between the two tensors, and show quantitatively that it increases as the density of the environment decreases. It implies that the proto-galaxies forming in the lower density regions should end up with having higher angular momentum than those in the higher density regions, which is consistent with recent numerical finding that the void and field galaxies have higher spin parameters than the cluster galaxies. Since the galaxy angular momentum plays a role of developing a disk-like structure and hindering the star-formation, our theoretical insight provides an answer to such fundamental observational question as why the large void galaxies have young stellar populations and high specific star formation rate, which was not explained by the previous morphology-density relation.