The alignment of galaxies at the Baryon Acoustic Oscillation scale

Massive elliptical galaxies align pointing towards each other in the structure of the Universe. Such alignments are well-described at large scales through a linear relation with respect to the tidal field of the large-scale structure. At such scales, galaxy alignments are sensitive to the presence of baryon acoustic oscillations (BAO). The shape of the BAO feature in galaxy alignment correlations differs from the traditional peak in the clustering correlation function. Instead, it appears as a trough feature at the BAO scale. In this work, we show that this feature can be explained by a simple toy model of tidal fields from a spherical shell of matter. This helps give a physical insight for the feature and highlights the need for tailored template-based identification methods for the BAO in alignment statistics. We also discuss the impact of projection baselines and photometric redshift uncertainties for identifying the BAO in intrinsic alignment measurements.