Abstract
Intrinsic alignments (IA) of galaxies, i.e. correlations of galaxy shapes with each other or with the density field, are a major astrophysical source of contamination for weak lensing surveys. We present the results of IA measurements of galaxies on 0.1- 200 Mpc/h scales using the SDSS-III BOSS LOWZ sample, in the redshift range 0.16<z<0.36. We extend the existing IA measurements for spectroscopic 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 color range of our sample, we observe no significant redshift or color dependence of IA. We measure the halo mass of LOWZ 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 variation 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 halos 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, which results in a null detection of large-scale intrinsic alignments for satellites. These results can be used to construct better intrinsic alignment models for removal of this contaminant to the weak lensing signal.
Highlights
The deflection of light rays due to the gravitational effects of matter, gravitational lensing, changes both the observed shape and size of distant galaxies
We fit these data to the following models: the galaxygalaxy correlation function calculated using non-linear matter power spectrum and linear galaxy bias, and the non-linear linear alignment (NLA) model at rp > 6h−1Mpc
We find that the NLA model fits the data well for rp > 6h−1Mpc, though there are significant deviations at smaller scales
Summary
The deflection of light rays due to the gravitational effects of matter, gravitational lensing, changes both the observed shape and size of distant galaxies. Intrinsic alignments of galaxies is perhaps the most important astrophysical systematic for weak lensing (for a review see, Troxel & Ishak 2014) It is the coherent alignments of the shapes of physically nearby galaxies which can mimic the weak lensing signal. One likely explanation for intrinsic alignments is that they are an environmental effect, whereby the local or large-scale tidal fields can shear and align the galaxy shapes, producing shape correlations. These correlations violate the assumption in weak lensing studies that observed correlations in galaxy shapes are only caused by gravitational lensing. These correlations violate the assumption in weak lensing studies that observed correlations in galaxy shapes are only caused by gravitational lensing. Hirata & Seljak (2004) developed the
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