Cosmological Information in the Intrinsic Alignments of Luminous Red Galaxies

TL;DR

This paper investigates how intrinsic galaxy alignments, especially of luminous red galaxies, encode cosmological information like BAO and primordial non-Gaussianity, using forecasts for current and future spectroscopic surveys.

Contribution

It provides the first detailed forecasts of the cosmological information in intrinsic alignments for upcoming galaxy surveys, focusing on BAO and non-Gaussianity constraints.

Findings

BAO signal in intrinsic alignments is marginally detectable in current surveys.

Future surveys like DESI and EUCLID will significantly improve BAO detection in alignments.

Primordial non-Gaussianity signals are weak and marginally detectable in intrinsic alignments.

Abstract

The intrinsic alignments of galaxies are usually regarded as a contaminant to weak gravitational lensing observables. The alignment of Luminous Red Galaxies, detected unambiguously in observations from the Sloan Digital Sky Survey, can be reproduced by the linear tidal alignment model of Catelan, Kamionkowski & Blandford (2001) on large scales. In this work, we explore the cosmological information encoded in the intrinsic alignments of red galaxies. We make forecasts for the ability of current and future spectroscopic surveys to constrain local primordial non-Gaussianity and Baryon Acoustic Oscillations (BAO) in the cross-correlation function of intrinsic alignments and the galaxy density field. For the Baryon Oscillation Spectroscopic Survey, we find that the BAO signal in the intrinsic alignments is marginally significant with a signal-to-noise ratio of 1.8 and 2.2 with the current LOWZ and CMASS samples of galaxies, respectively, and increasing to 2.3 and 2.7 once the survey is completed. For the Dark Energy Spectroscopic Instrument and for a spectroscopic survey following the EUCLID redshift selection function, we find signal-to-noise ratios of 12 and 15, respectively. Local type primordial non-Gaussianity, parametrized by fNL = 10, is only marginally significant in the intrinsic alignments signal with signal-to-noise ratios < 2 for the three surveys considered.