The Nonlinear Evolution of Galaxy Intrinsic Alignments

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.