Cosmo-26

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

Not scheduled

20m

Gorlaeus gebouw (Leiden University)

Talk Large-Scale Structure

Speaker

Pedro da Silveira Ferreira (Zhejiang University)

Description

We present evidence for a large-scale axial intrinsic alignment (LAIA), a coherent preferred orientation shared by galaxies and cosmic-web filaments. LAIA provides a new statistical-isotropy test based on the orientation field of galaxy-scale and filamentary structures, complementary to CMB- and large-scale-structure-based probes of the cosmological principle. Applying a new estimator to the Dark Energy Survey Year 3 weak-lensing shape catalog, we reconstruct the galaxies' orientation field and identify a coherent preferred axis on dipolar angular scales. Spirals' semi-minor axes and ellipticals' semi-major axes point toward a common direction, with a morphology-dependent amplitude hierarchy consistent with tidal-torquing physics. We further extend the analysis beyond galaxy shapes by measuring a consistent axial pattern in cosmic-web filament orientations from SDSS, providing an independent and physically distinct tracer of the underlying large-scale tidal field. Remarkably, because the DES and SDSS footprints are substantially different, the agreement is not driven by the galaxies and filaments occupying the same local environments. Instead, it points to a common large-scale axial pattern traced independently by galaxy morphologies and by the cosmic web. Their statistical compatibility with the galaxy-based preferred axis therefore provides a non-local, cross-survey, and cross-observable consistency test, rather than a simple measurement of galaxy--host-filament alignment. The signal disfavors the null hypothesis at approximately $4\sigma$, persists across spatial and redshift splits, and remains robust against a broad suite of realistic survey-systematics tests. We validate the estimator and assess the physical interpretation using N-body-based mock catalogs, including Euclid Flagship 2 and MICECAT v2 with intrinsic alignments. If confirmed, LAIA would reveal a statistically significant preferred axis in the orientation field of galaxies and filaments, potentially tracing a large-scale tidal field imprinted during structure formation. This work introduces a new observational bridge between galaxy evolution, intrinsic alignments, cosmic-web physics, weak-lensing systematics, and tests of statistical isotropy, offering a compass that links morphology, angular momentum, environment, and cosmology.