Collision between molecular clouds IV: The role of feedback and magnetic field in head on collisions

Abstract

We systematically investigate how cloud-cloud collisions influence star formation, emphasizing the roles of collision velocity, magnetic field orientation, and radiative feedback. Using the first cloud-cloud collision simulations that model individual star formation and accretion with all stellar feedback mechanisms, we explore the morphological evolution, star formation efficiency (SFE), fragmentation, stellar mass distribution, and feedback-driven gas dispersal. Our results show that cloud collisions substantially enhance the rate and timing of star formation compared to isolated scenarios, though the final SFE remains broadly similar across all setups. Lower collision velocities facilitate prolonged gravitational interaction and accumulation of gas, promoting sustained star formation characterized by elongated filamentary structures. Conversely, high-velocity collisions induce rapid gas compression and turbulent motions, leading to intense but transient episodes of star formation, which are curtailed by feedback-driven dispersal. The orientation of the magnetic field markedly affects collision outcomes. Parallel fields allow gas to collapse efficiently along magnetic lines, forming fewer but more massive stars. In contrast, perpendicular fields generate significant magnetic pressure, which stabilizes the shock-compressed gas and delays gravitational collapse, resulting in more distributed and less massive stellar fragments. Radiative feedback from massive stars consistently regulates star formation, halting further gas accretion at moderate efficiencies (10-15%) and initiating feedback-driven dispersal. Although the cloud dynamics vary significantly, the stellar mass function remains robust across scenarios-shaped modestly by magnetic orientation but only weakly influenced by collision velocity.

Figures (14)

• Figure 1: Projected gas surface density evolution for the 1x perpendicular magnetic field collision scenario at three representative evolutionary stages (early, intermediate, and late times). Each panel highlights how the perpendicular magnetic field shapes the morphology, initially stabilizing the gas layer against fragmentation and ultimately facilitating a dramatic feedback-driven dispersal in later stages.
• Figure 2: Position–velocity diagrams for the 1x perpendicular magnetic field collision scenario at the same evolutionary stages depicted in \ref{['fig:1xproj']}. These diagrams illustrate how the velocity structure evolves from two initially distinct clouds through turbulent mixing in the intermediate stage to a highly dispersed, feedback-influenced velocity field at late times, highlighting the complex interplay between magnetic fields, gas dynamics, and stellar feedback.
• Figure 3: Projected gas surface density evolution for the 5x perpendicular magnetic field collision scenario at three representative evolutionary stages (early, intermediate, and late times). Each panel highlights how the perpendicular magnetic field shapes the morphology, initially stabilizing the gas layer against fragmentation and ultimately facilitating a dramatic feedback-driven dispersal in later stages.
• Figure 4: Position–velocity diagrams for the 5x perpendicular magnetic field collision scenario at the same evolutionary stages depicted in \ref{['fig:5xproj']}. These diagrams illustrate how the velocity structure evolves from two initially distinct clouds through turbulent mixing in the intermediate stage to a highly dispersed, feedback-influenced velocity field at late times, highlighting the complex interplay between magnetic fields, gas dynamics, and stellar feedback.
• Figure 5: Projected gas surface density evolution for the 1z parallel magnetic field collision scenario at three representative evolutionary stages (early, intermediate, and late times). Each panel highlights how the perpendicular magnetic field shapes the morphology, initially stabilizing the gas layer against fragmentation and ultimately facilitating a dramatic feedback-driven dispersal in later stages.