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

TL;DR

This paper reports the first detection of large-scale axial intrinsic alignment of galaxies using DES data, revealing a potential preferred cosmic direction and offering insights into galaxy evolution and cosmology.

Contribution

It introduces a new estimator to map galaxy orientations and reports the first measurement of large-scale axial intrinsic alignment in the universe.

Findings

Detection of large-scale axial intrinsic alignment on dipolar scales

Galaxies' axes coherently point toward a common direction

Alignment pattern consistent with primordial tidal field influence

Abstract

Applying a new estimator to the Dark Energy Survey (DES) Y3 weak lensing shape catalog, we map the galaxies' orientation field and report the first detection of a large-scale axial intrinsic alignment (LAIA) on dipolar angular scales. Ellipticals' semi-major axes and spirals' semi-minor axes coherently point toward a common direction, (RA,Dec)=$(306^{+6}_{-4},52^{+3}_{-3})^\circ$ and $(296^{+10}_{-18},50^{+6}_{-2})^\circ$, respectively, with amplitudes in the expected tidal-torquing hierarchy. This pattern could be produced by a horizon-scale tidal field imprinted by primordial inhomogeneities during galaxy assembly and, if confirmed, would signal a statistically significant preferred direction in the Universe, thereby probing deviations from statistical isotropy. The signal persists across spatial and redshift splits and is difficult to attribute to survey systematics. LAIA offers a new sky-wide compass linking galaxy evolution and cosmology.