Intrinsic alignments of SDSS-III BOSS LOWZ sample galaxies

TL;DR

This study measures intrinsic galaxy alignments in the SDSS-III BOSS LOWZ sample across various scales, luminosities, and environments, providing insights to improve weak lensing analyses.

Contribution

It extends IA measurements to lower luminosity galaxies, explores their dependence on mass, luminosity, and environment, and highlights the need for flexible models to mitigate IA contamination.

Findings

Large-scale IA follows a power-law luminosity dependence.

No significant redshift or color dependence observed.

Group central galaxies are aligned with halos and tidal fields.

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.