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Galaxy intrinsic alignments (IAs) have long been recognised as a significantcontaminant to weak lensing-based cosmological inference. In this paper we seekto quantify the impact of a common modelling assumption in analyticdescriptions of intrinsic alignments: that of spherically symmetric dark matterhalos. Understanding such effects is important as the current generation ofintrinsic alignment models are known to be limited, particularly on smallscales, and building an accurate theoretical description will be essential forfully exploiting the information in future lensing data. Our analysis is basedon a catalogue of 113,560 galaxies between $z=0.06-1.00$ from MassiveBlack-II,a hydrodynamical simulation of box length $100 h^{-1}$ Mpc. We find satelliteanisotropy contributes at the level of $\geq 30-40\%$ to the small scalealignment correlation functions. At separations larger than $1 h^{-1}$ Mpc theimpact is roughly scale-independent, inducing a shift in the amplitude of theIA power spectra of $\sim20\%$. These conclusions are consistent across theredshift range and between the MassiveBlack-II and Illustris simulations. Thecosmological implications of these results are tested using a simulatedlikelihood analysis. Synthetic cosmic shear data is constructed with theexpected characteristics (depth, area and number density) of a future LSST-likesurvey. Our results suggest that modelling alignments using a halo model basedupon spherical symmetry could potentially induce cosmological parameter biasesat the $\sim 1.5\sigma$ level for $S_8$ and $w$.

Testing the Impact of Satellite Anisotropy on Large and Small Scale Intrinsic Alignments using Hydrodynamical Simulations