Living with Neighbors. V. Better-aligned Spiral+Spiral Galaxy Pairs Show Stronger Star Formation

Abstract

Enhanced star formation (SF) with star-forming neighboring galaxies bolsters hydrodynamical contributions during paired interactions. Although the relative spin orientation between interacting galaxies can influence this effect, it has not been comprehensively explored. In this study, using a curated sample of nearby (0.02 < z < 0.06) spiral-spiral pairs and an isolated control sample from the Sloan Digital Sky Survey Data Release 7, coupled with Galaxy Zoo 2, and a method to estimate spin-spin alignment (SSA), we systematically compare the impact of the relative orientation, $\cos\xi$, on interaction-induced SF. We find that SSA is a key factor alongside the conventional parameters of projected separation and the SF of neighboring galaxies. The SF enhancement increases as configurations transition from perpendicular ($\cos\xi \sim 0$) to well aligned ($\cos\xi > 0.7$). The effect is strongest when neighboring galaxies have higher SF, indicating a hydrodynamical origin. The trend is consistent with increased hydrodynamical friction via stronger ram pressure and a higher likelihood of prograde orbits in well-aligned pairs.