Galactic structure dependence of cloud-cloud collisions 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 ($v_{\mathrm{col}}$) and lower GMC mass ($M_{\mathrm{GMC}}$) or/and density ($\hat{I}{\pounds }_{\mathrm{GMC}}$) tend to suppress star formation. In this study, we choose the nearby barred galaxy NGC 3627 to examine the SFR and SFE of a colliding GMC ($m_{\mathrm{CCC}}^{\star }$ and $\hat{I}{\mu }_{\mathrm{CCC}}$) and explore the connections between $m_{\mathrm{CCC}}^{\star }$ and $\hat{I}{\mu }_{\mathrm{CCC}}$, $M_{\mathrm{GMC}}$($\hat{I}{\pounds }_{\mathrm{GMC}}$) and $v_{\mathrm{col}}$, and galactic structures (disk, bar, and bar-end). Using ALMA CO(2--1) data (60~pc resolution), we estimated $v_{\mathrm{col}}$ 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 $m_{\mathrm{CCC}}^{\star }$ and $\hat{I}{\mu }_{\mathrm{CCC}}$ using attenuation-corrected H$\hat{I}\pm$ data from VLT MUSE. We found that both $m_{\mathrm{CCC}}^{\star }$ and $\hat{I}{\mu }_{\mathrm{CCC}}$ are lower in the bar (median values: $10^{3.84}{M}_{\odot }$ and $0.18\%$), and higher in the bar-end ($10^{4.89}{M}_{\odot }$ and $1.10\%$) compared to the disk ($10^{4.28}{M}_{\odot }$ and $0.75\%$). Furthermore, we found that structural differences within the parameter space of $v_{\mathrm{col}}$ and $M_{\mathrm{GMC}}$($\hat{I}{\pounds }_{\mathrm{GMC}}$), with higher $M_{\mathrm{GMC}}$($\hat{I}{\pounds }_{\mathrm{GMC}}$) in the bar-end and higher $v_{\mathrm{col}}$ 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 that variations in CCC properties across different galactic structures can explain the observed differences in SFE on a kpc scale within a disk galaxy.

20 pages, 8 figures, accepted for publication in ApJ