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

TL;DR

This study shows that spiral galaxy pairs with better spin alignment exhibit stronger star formation, highlighting the role of hydrodynamical effects and orbital orientation in galaxy interactions.

Contribution

It introduces a systematic analysis of spin-spin alignment's impact on star formation enhancement in galaxy pairs using SDSS data and Galaxy Zoo 2.

Findings

Star formation increases with better spin alignment.

Aligned pairs show stronger hydrodynamical effects.

Prograde orbits are more common in well-aligned pairs.

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.