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

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What is this paper about ?

AI: This paper is about inferring the linear alignment amplitude and ellipticity variance in the context of the galaxy intrinsic alignment model. It discusses the methodology of using a fully Bayesian approach to constrain the linear alignment model using galaxy shape measurements and three-dimensional tidal fields. The paper also presents the analysis of the linear alignment amplitude posterior moments and variance, as well as its evolution with redshift and color in a sample of luminous red galaxies. Additionally, it proposes a model and correction for the scale-dependent linear alignment amplitude in the presence of random noise and filtering effects, and validates the algorithm using mock data.


Eleni Tsaprazi, Nhat-Minh Nguyen, Jens Jasche, Fabian Schmidt, Guilhem Lavaux


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$h^{-1}\;\mathrm{Mpc}$.

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