Galactic Structure Dependence of Cloud–Cloud-collision-driven Star Formation in the Barred Galaxy NGC 3627

Abstract

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 H α 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 ^3.84 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 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.

Keywords

• Star formation
• Interstellar medium
• Molecular gas
• Giant molecular clouds
• Barred spiral galaxies