Intrinsic alignment of simulated galaxies in the cosmic web: implications for weak lensing surveys

TL;DR

This study investigates the intrinsic alignments of simulated galaxies within the cosmic web, revealing mass- and color-dependent alignments and their potential impact on weak lensing surveys.

Contribution

It provides the first detailed analysis of intrinsic galaxy alignments using high-resolution hydrodynamical simulations, highlighting implications for cosmic shear measurements.

Findings

Low-mass galaxies' spins align with filament directions

High-mass galaxies' spins are perpendicular to filaments and walls

Blue galaxies show stronger correlation with tidal fields

Abstract

The intrinsic alignment of galaxy shapes (by means of their angular momentum) and their cross-correlation with the surrounding dark matter tidal field are investigated using the 160 000, z=1.2 synthetic galaxies extracted from the high-resolution cosmological hydrodynamical simulation Horizon-AGN. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and colour. For the low-mass galaxies, this spin is locally aligned with the tidal field `filamentary' direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of our synthetic catalog are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to 10 Mpc/h comoving distance. We also report a correlation of the projected ellipticities of blue, intermediate mass galaxies on a similar scale at a level of 10^(-4) which could be a concern for cosmic shear measurements. We do not report any measurable intrinsic alignments of the reddest galaxies of our sample. This work is a first step toward the use of very realistic catalog of synthetic galaxies to evaluate the contamination of weak lensing measurement by the intrinsic galactic alignments.