Galactic structure dependence of cloud-cloud collisions driven star formation in NGC3627

While cloud-cloud collisions (CCCs) have been proposed as a mechanism for triggering massive star formation (SF), it is suggested that higher collision velocities (vcol) and lower GMC mass (MGMC) or/and density (ΣGMC) tend to suppress SF. In this study, we choose the nearby barred galaxy NGC 3627 to examine the SFR and SFE of a colliding GMC (m* and ε) and explore the connections between m* and ε, MGMC(ΣGMC) and vcol, and galactic structures (disk, bar, and bar-end). Using ALMA CO(2–1) data (60 pc resolution), we estimated vcol 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 SF, and then calculated m* and ε using attenuation-corrected Hα data from VLT MUSE. We found that both m⋆CCC and ε are lower in the bar (median values: 10^3.84 M⊙ and 0.18%), and higher in the bar-end (10^4.89 M⊙ and 1.10%) compared to the disk (10^4.28 M⊙ and 0.75%). Furthermore, we found that structural differences within the parameter space of vcol and MGMC(ΣGMC), with higher MGMC(ΣGMC) in the bar-end and higher vcol in the bar compared to the disk, lead to higher SF activity in the bar-end and lower activity in the bar. Our results support the scenario that variations in CCC properties across different galactic structures can explain the observed differences in SFE on a kpc scale within a disk galaxy.