| Summary: | <p>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, <em>z</em> = 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 <em>locally</em> aligned with the tidal field ‘filamentary’ direction while, for the high-mass galaxies, it is <em>perpendicular</em> to both filaments and walls. The bluest galaxies of our synthetic catalogue are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to ∼10 <em>h</em><sup>− 1</sup> Mpc 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<sup>−4</sup> 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 towards the use of very realistic catalogue of synthetic galaxies to evaluate the contamination of weak lensing measurement by the intrinsic galactic alignments.</p>
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