Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys

Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright galaxies in Sloan Digital Sky Survey (SDSS) data. Here we present a more detailed characterization of this effect, which can cause anticorrelations between gravitational lensing shear and intrinsic ellipticity (GI correlations). This measurement uses 36 278 luminous red galaxies (LRGs) from the SDSS spectroscopic sample with 0.15 <z <0.35, split by redshift and luminosity; 7758 LRGs from the 2dF-SDSS LRG and QSO (2SLAQ) survey at 0.4 <z <0.8; and a variety of other SDSS samples from previous, related work. We find >3I? detections of the effect on large scales (up to 60 h-1 Mpc) for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ sample, we find a 2I? detection for a bright subsample, and no detection for a fainter subsample.