The MAGPI Survey: the evolution of galaxy spin–filament alignments since z∼0.3

We present measurements of galaxy spin-filament alignments at 0.20 < z < 0.42 using the MAGPI Survey, exploiting resolved stellar and ionised gas kinematics to reconstruct 3D spin axes. Cosmic filaments are identified using a stellar mass-matched constant-number-density population from the GAMA, MAGPI Redshift Survey and DESI datasets. We detect a flipping of the statistical alignment signal at z ∼ 0.3 as a function of M⋆: low-mass galaxies preferentially exhibit spins parallel to the direction of their host filaments, while high-mass galaxies tend towards perpendicular orientations. The transition mass is measured to be log (M⋆, t/M⊙) ≃ 10.8, approximately 0.6 dex higher than the value for the SAMI Galaxy Survey at z ∼ 0.05. Bootstrap analysis gives 99.5% confidence that the transition mass is higher for MAGPI than SAMI. At fixed stellar mass MAGPI galaxies exhibit stronger parallel alignments than their SAMI counterparts, suggesting evolution of spin–filament alignments over the past ∼ 3 Gyr. The gaseous component in MAGPI galaxies is more closely aligned with filaments than the stellar component, relative to a M⋆-matched SAMI sample. This indicates a stronger coupling between ionised gas and the large-scale structure at z ∼ 0.3, consistent with coherent gas accretion onto filaments remaining efficient at higher M⋆. At z ∼ 0 we detect a transition toward perpendicular alignments at lower M⋆, while the gas and stellar components exhibit similar alignments relative to filaments, likely due to the cumulative effects of mergers and secular evolution.