Full-sky ray-tracing simulation of weak lensing using ELUCID simulations: exploring galaxy intrinsic alignment and cosmic shear correlations

摘要

The intrinsic alignment of galaxies is an important systematic effect inweak-lensing surveys, which can affect the derived cosmological parameters. Onedirect way to distinguish different alignment models and quantify their effectson the measurement is to produce mocked weak-lensing surveys. In this work, weuse full-sky ray-tracing technique to produce mock images of galaxies from theELUCID $N$-body simulation run with the WMAP9 cosmology. In our model we assumethat the shape of central elliptical galaxy follows that of the dark matterhalo, and spiral galaxy follows the halo spin. Using the mocked galaxy images,a combination of galaxy intrinsic shape and the gravitational shear, we comparethe predicted tomographic shear correlations to the results of KiDS and DLS. Itis found that our predictions stay between the KiDS and DLS results. We ruleout a model in which the satellite galaxies are radially aligned with thecenter galaxy, otherwise the shear-correlations on small scales are too high.Most important, we find that although the intrinsic alignment of spiralgalaxies is very weak, they induce a positive correlation between thegravitational shear signal and the intrinsic galaxy orientation (GI). This isbecause the spiral galaxy is tangentially aligned with the nearby large-scaleoverdensity, contrary to the radial alignment of elliptical galaxy. Our resultsexplain the origin of detected positive GI term from the weak-lensing surveys.We conclude that in future analysis, the GI model must include the dependenceon galaxy types in more detail. And the full-sky mock data introduced in thiswork can be available if you are interesting.