The Gravitational Shear--Intrinsic Ellipticity Correlation Functions of Luminous Red Galaxies in Observation and in the $\Lambda$CDM Model

TL;DR

This study measures and models the gravitational shear--intrinsic ellipticity correlation of luminous red galaxies, confirming the model with a Gaussian misalignment distribution and providing insights for weak lensing survey analyses.

Contribution

It accurately measures the GI correlation in SDSS data and demonstrates that a Gaussian misalignment model with a specific angle explains the observations within the b3CDM framework.

Findings

GI correlation is consistent with a Gaussian misalignment angle of ~35 degrees.

A correlation exists between galaxy axis ratios and intrinsic alignments.

The results inform modeling of weak lensing systematics.

Abstract

We examine whether the gravitational shear--intrinsic ellipticity (GI) correlation function of the luminous red galaxies (LRGs) can be modeled with the distribution function of a misalignment angle advocated recently by Okumura et al. For this purpose, we have accurately measured the GI correlation for the LRGs in the Data Release 6 (DR6) of the Sloan Digital Sky Survey (SDSS), which confirms the results of Hirata et al. who used the DR4 data. By comparing the GI correlation functions in the simulation and in the observation, we find that the GI correlation can be modeled in the current $\Lambda$CDM model if the misalignment follows a Gaussian distribution with a zero mean and a typical misalignment angle $\sigma_\theta=34.9^{+1.9}_{-2.1}$ degrees. We also find a correlation between the axis ratios and intrinsic alignments of LRGs. This effect should be taken into account in theoretical modeling of the GI and intrinsic ellipticity--ellipticity correlations for weak lensing surveys.