Distinguishing between ΛCDM and f(R) gravity models using halo ellipticity correlations in simulations

ABSTRACT There is a growing interest in utilizing intrinsic alignment (IA) of galaxy shapes as a geometric and dynamical probe of cosmology. In this paper, we present the first measurements of IA in a modified gravity model using the gravitational shear-intrinsic ellipticity correlation (GI) and intrinsic ellipticity-ellipticity correlation (II) functions of dark-matter haloes from f (R) gravity simulations. By comparing them with the same statistics measured in Lambda cold dark matter (ΛCDM) simulations, we find that the IA statistics in different gravity models show distinguishable features, with a trend similar to the case of conventional galaxy clustering statistics. Thus, the GI and II correlations are found to be useful in distinguishing between the ΛCDM and f (R) gravity models. More quantitatively, IA statistics enhance detectability of the imprint of f (R) gravity on large-scale structures by 40{\ per\ cent} when combined with the conventional halo clustering in redshift space. We also find that the correlation between the axial ratio and orientation of haloes becomes stronger in f (R) gravity than that in ΛCDM. Our results demonstrate the usefulness of IA statistics as a probe of gravity beyond a consistency test of ΛCDM and general relativity.