Where Galaxies Point: First Measurement of the Large-Scale Axial Intrinsic Alignment

Pedro da Silveira Ferreira; Rafael Oliveira Ramos; Paula S. Ferreira; Arianna Cortesi; Fabricio Ferrari; Valerio Marra; Clécio R. Bom; Renyue Cen

arXiv · 2511.10005

Where Galaxies Point: First Measurement of the Large-Scale Axial Intrinsic Alignment

Pedro da Silveira Ferreira·Rafael Oliveira Ramos·Paula S. Ferreira·Arianna Cortesi·Fabricio Ferrari·Valerio Marra·Clécio R. Bom·Renyue Cen

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Abstract

We report evidence for large-scale axial intrinsic alignment (LAIA): a coherent axis shared by galaxies and cosmic-web filaments. Applying an orientation-field estimator to Dark Energy Survey (DES) Y3 shape data, we identify a preferred axis in galaxy orientations. Ellipticals' semi-major and spirals' semi-minor axes align with it, producing a $4.7\sigma$ signal whose pattern and amplitude hierarchy are consistent with morphology-dependent tidal-alignment and tidal-torquing expectations. Independently, Sloan Digital Sky Survey (SDSS) filament catalogues yield a compatible axis: northern and southern Galactic samples agree within $\simeq1\sigma$, the combined signal reaches $12.6\sigma$, and the axis lies within $\simeq2\sigma$ of the high-redshift galaxy sample direction. Because DES and SDSS footprints overlap marginally, this agreement is unlikely to arise from direct galaxy--filament alignment. It therefore provides a multi-survey, multi-observable test of a large-scale orientation field, stable under redshift and systematics tests. $N$-body mocks based on an isotropic $\Lambda$CDM cosmology with standard intrinsic-alignment prescriptions, including Euclid Flagship 2 and MICECAT v2, do not reproduce the pattern. LAIA provides a new statistical-isotropy probe linking galaxy morphology, cosmic-web structure and large-scale tidal fields.

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Pedro da Silveira Ferreira, Rafael Oliveira Ramos, Paula S. Ferreira, Arianna Cortesi, Fabricio Ferrari, Valerio Marra, Clécio R. Bom, Renyue Cen. 2025-11-13. Where Galaxies Point: First Measurement of the Large-Scale Axial Intrinsic Alignment. https://arxiv.org/abs/2511.10005

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