2025ApJ...981..156M

While cloud-cloud collisions (CCCs) have been proposed as a mechanism for triggering massive star formation, it is suggested that higher collision velocities (v_col) and lower giant molecular cloud (GMC) mass (M_GMC) and/or density (Σ_GMC) tend to suppress star formation. In this study, we choose the nearby barred galaxy NGC 3627 to examine the star formation rate and star formation efficiency (SFE) of a colliding GMC (${m}_{{\rm{CCC}}}^{\star }$ and ϵ_CCC) and explore the connections between ${m}_{{\rm{CCC}}}^{\star }$ and ϵ_CCC, M_GMC(Σ_GMC) and v_col, and galactic structures (disk, bar, and bar end). Using Atacama Large Millimeter/submillimeter Array CO (2-1) data (60 pc resolution), we estimated v_col within 500 pc apertures, based on line-of-sight GMC velocities, assuming random motion in a two-dimensional plane. We extracted apertures where at least 0.1 collisions occur per 1 Myr, identifying them as regions dominated by CCC-driven star formation, and then calculated ${m}_{{\rm{CCC}}}^{\star }$ and ϵ_CCC using attenuation-corrected Hα data from MUSE on the Very Large Telescope. We found that both ${m}_{{\rm{CCC}}}^{\star }$ and ϵ_CCC are lower in the bar (median values: 10^3.84M_⊙ and 0.18%) and higher in the bar end (10^4.89M_⊙ and 1.10%) compared to the disk (10^4.28M_⊙ and 0.75%). Furthermore, we found that structural differences within the parameter space of v_col and M_GMC(Σ_GMC), with higher M_GMC(Σ_GMC) in the bar end and higher v_col in the bar compared to the disk, lead to higher star formation activity in the bar end and lower activity in the bar. Our results support the scenario in which variations in CCC properties across different galactic structures can explain the observed differences in SFE on a kiloparsec scale within a disk galaxy.