A Perturbative Treatment of Intrinsic Alignments

Intrinsic alignments (IA), correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in weak lensing and a probe of the effect of large-scale structure on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy. Previous models for IA fall broadly into two categories: linear alignment models, which are linear in the matter density field, and tidal torquing models, which are quadratic in the matter density. More generally, these contributions can be considered part of an effective expansion in all potentially relevant cosmological fields at a given order. I have developed a full, self-consistent formalism up to third order in standard perturbation theory (SPT) for such a perturbative treatment of the IA field, analogous to the use of bias coefficients to quantify clustering. I will present this model and discuss the implications for weak lensing systematics as well as for studies of galaxy formation and evolution. This work includes a complete treatment of time-evolution effects, which is not only required for a self-consistent SPT expansion, but also allows for the use of IA to probe properties of galaxy formation.

Speaker: Denise Schmitz, Caltech