Three-point intrinsic alignments of dark matter haloes in the IllustrisTNG simulation

Abstract

ABSTRACT We use the IllustrisTNG suite of cosmological simulations to measure intrinsic alignment (IA) bispectra of dark matter subhaloes between redshifts 0 and 1. We decompose the intrinsic shear field into E- and B- modes and find that the bispectra BδδE and BδEE, between the matter overdensity field, δ, and the E-mode field, are detected with high significance. We also model the IA bispectra analytically using a method consistent with the two-point non-linear alignment model. We use this model and the simulation measurements to infer the IA amplitude AIA and find that values of AIA obtained from IA power spectra and bispectra agree well at scales up to $k_\mathrm{max}= 2 \, h \mathrm{Mpc}^{-1}$. For example at z = 1, AIA = 2.13 ± 0.02 from the cross power spectrum between the matter overdensity and E-mode fields and AIA = 2.11 ± 0.03 from BδδE. This demonstrates that a single physically motivated model can jointly model two-point and three-point statistics of IAs, thus enabling a cleaner separation between IAs and cosmological weak lensing signals.