Galaxy Zoo: a correlation between the coherence of galaxy spin chirality and star formation efficiency

We report on the finding of a correlation between the past star formation activity of galaxies and the degree to which the rotation axes of neighbouring galaxies are aligned. This is obtained by cross-correlating star formation histories, derived using the multiple optimized parameter estimation and data compression (MOPED) algorithm, and the spatial coherence of spin direction (chirality), as determined by the Galaxy Zoo project, for a sample of Sloan Digital Sky Survey (SDSS) galaxies. Our findings suggest that spiral galaxies, which formed the majority of their stars early (z > 2), tend to display coherent rotation over scales of ∼10 Mpc h⁻¹. The correlation is weaker for galaxies with significant recent star formation. We find evidence for this alignment at more than the 5σ level, but no correlation with other galaxy stellar properties. This finding can be explained within the context of hierarchical tidal-torque theory if the SDSS galaxies harbouring the majority of the old stellar population were formed in the past, in the same filament and at about the same time. Galaxies with significant recent star formation instead are in the field, thus influenced by the general tidal field that will align them in random directions, or have had a recent merger that would promote star formation but change the spin direction.