CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment

We present weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment. Using data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), we measure the weighted-average ratio of the aligned projected ellipticity components of galaxy matter haloes and their embedded galaxies, f_h, split by galaxy type. We then compare our observations to measurements taken from the Millennium Simulation, assuming different models of galaxy-halo misalignment. Using the Millennium Simulation, we verify that the statistical estimator used removes contamination from cosmic shear. We also detect an additional signal in the simulation, which we interpret as the impact of intrinsic shape-shear alignments between the lenses and their large-scale structure environment. These alignments are likely to have caused some of the previous observational constraints on f_h to be biased high. From CFHTLenS, we find f_h = -0.04 ± 0.25 for early-type galaxies, which is consistent with current models for the galaxy-halo misalignment predicting f_h ≃ 0.20. For late-type galaxies we measure f_h=0.69_{-0.36}^{+0.37} from CFHTLenS. This can be compared to the simulated results which yield f_h ≃ 0.02 for misaligned late-type models.