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 protogalaxy is generated to first order by the misalignment between the protogalaxy's inertia tensor and the local tidal tensor. Then we quantify analytically the degree of misalignment between the two tensors and show quantitatively that it increases as the density of the environment decreases. This implies that protogalaxies forming in lower density regions should end up with higher angular momentum than those in higher density regions, which is consistent with the recent numerical finding that void and field galaxies have higher spin parameters than do cluster galaxies. Since the galaxy angular momentum plays a role in developing a disklike structure and hindering star formation, our theoretical insight provides an answer to such a fundamental observational question as why the large void galaxies have young stellar populations and high specific star formation rates, which was not explained by the previous morphology-density relation.