The Nonlinear Evolution of Galaxy Intrinsic Alignments

TL;DR

This paper models and detects the nonlinear contribution to galaxy intrinsic alignments caused by non-Gaussian density fluctuations, revealing significant spin correlations on large scales and their dependence on halo properties.

Contribution

It introduces a linear scaling model for nonlinear halo spin alignments and provides empirical detection of nonlinear tidal effects using Millennium Run simulation data.

Findings

Detection of spin correlations up to 10 Mpc/h at z=0

Nonlinear effects increase with decreasing halo mass and specific angular momentum

Nonlinear tidal effects are significant for understanding intrinsic alignments

Abstract

The non-Gaussian contribution to the intrinsic halo spin alignments is analytically modeled and numerically detected. Assuming that the growth of non-Gaussianity in the density fluctuations caused the tidal field to have nonlinear-order effect on the orientations of the halo angular momentum, we model the intrinsic halo spin alignments as a linear scaling of the density correlations on large scales, which is different from the previous quadratic-scaling model based on the linear tidal torque theory. Then, we analyze the halo catalogs from the recent high-resolution Millennium Run simulation at four different redshifts (z=0,0.5,1 and 2) and measure quantitatively the degree of the nonlinear effect on the halo spin alignments and its changes with redshifts. A clear signal of spin correlations is found on scales as large as 10 Mpc/h at z=0, which marks a detection of the nonlinear tidal effect on the intrinsic halo alignments. We also investigate how the nonlinear effect depends on the intrinsic properties of the halos. It is found that the degree of the nonlinear tidal effect increases as the halo mass scale decreases, the halo specific angular momentum increases, and the halo peculiar velocity decreases. We discuss implication of our result on the weak gravitational lensing.