Field-level inference of galaxy intrinsic alignment from the SDSS-III BOSS survey

TL;DR

This study uses a Bayesian field-level approach to analyze galaxy shapes and tidal fields from SDSS-III BOSS data, providing new constraints on intrinsic galaxy alignments relevant for cosmology.

Contribution

It introduces a fully Bayesian field-level method to constrain the linear alignment model using SDSS-III BOSS galaxy data and tidal field reconstructions.

Findings

Detected 4σ evidence of intrinsic alignment.

Measured alignment amplitude of $A_I=2.9 1.7$ at 20$h^{-1}$ Mpc.

Demonstrated the effectiveness of Bayesian field-level inference for galaxy alignments.

Abstract

As a large-scale overdensity collapses, it affects the orientation and shape of galaxies that form, by exerting tidal shear along their axes. Therefore, the shapes of elliptical galaxies align with the tidal field of cosmic structures. This intrinsic alignment provides insights into galaxy formation and the primordial universe, complements late-time cosmological probes and constitutes a significant systematic effect for weak gravitational lensing observations. In the present study, we provide constraints on the linear alignment model using a fully Bayesian field-level approach, using galaxy shape measurements from the SDSS-III BOSS LOWZ sample and three-dimensional tidal fields constrained with the LOWZ and CMASS galaxy samples of the SDSS-III BOSS survey. We find 4$\sigma$ evidence of intrinsic alignment, with an amplitude of $A_I=2.9 \pm 0.7$ at 20$h^{-1}\;\mathrm{Mpc}$.