Intrinsic alignments in IllustrisTNG and their implications for weak lensing: Tidal shearing and tidal torquing mechanisms put to the test

ABSTRACT Accurate measurements of the cosmic shear signal require a separation true weak gravitational lensing from intrinsic shape correlations galaxies. These ‘intrinsic alignments’ galaxies originate galaxy formation processes and are expected to be correlated with field through tidal affecting galaxies, such as shearing for elliptical torquing spiral In this study, we use morphologically selected samples illustrisTNG simulation at z = 0 1 test commonly employed linear (tidal shearing) quadratic torquing) models alignments. We obtain local alignment parameters, including corrections large-scale anisotropies cosmologically small volume, study their dependence on environmental properties. find significant (linear model), that increases mass redshift. Spiral (quadratic other hand, exhibit only most massive objects 1. show model break down its fundamental assumptions, simultaneously align according model. derived parameters compute spectra estimate contamination in obtained by Euclid.