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