Intrinsic alignments of SDSS-III BOSS LOWZ sample galaxies

Intrinsic alignments (IA) of galaxies, i.e. correlations of galaxy shapes with each other (II) or with the density field (gI), are potentially a major astrophysical source of contamination for weak lensing surveys. We present the results of IA measurements of galaxies on 0.1–200 h−1 Mpc scales using the SDSS-III BOSS low-redshift (LOWZ) sample, in the redshift range 0.16 z < 0.36. We extend the existing IA measurements for spectroscopic luminous red galaxies (LRGs) to lower luminosities, and show that the luminosity dependence of large-scale IA can be well described by a power law. Within the limited redshift and colour range of our sample, we observe no significant redshift or colour dependence of IA. We measure the halo mass of galaxies using galaxy–galaxy lensing, and show that the mass dependence of large-scale IA is also well described by a power law. We detect variations in the scale dependence of IA with mass and luminosity, which underscores the need to use flexible templates in order to remove the IA signal. We also study the environment dependence of IA by splitting the sample into field and group galaxies, which are further split into satellite and central galaxies. We show that group central galaxies are aligned with their haloes at small scales and also are aligned with the tidal fields out to large scales. We also detect the radial alignments of satellite galaxies within groups. These results can be used to construct better IA models for removal of this contaminant to the weak lensing signal.