Environmental regulation of cloud and star formation in galactic bars

TL;DR

This study uses high-resolution simulations to investigate how galactic bar dynamics influence molecular cloud formation and star formation, revealing a dichotomy between bar sides and the impact of orbital crowding on starburst activity.

Contribution

It provides new insights into the role of bar dynamics at multiple scales in regulating star formation and molecular cloud evolution in galaxies.

Findings

Enhanced star formation at bar extremities due to orbital crowding.

Strong dichotomy in cloud fragmentation between leading and trailing sides.

Bar dynamics can decouple young stars from their parent clouds.

Abstract

The strong time-dependence of the dynamics of galactic bars yields a complex and rapidly evolving distribution of dense gas and star forming regions. Although bars mainly host regions void of any star formation activity, their extremities can gather the physical conditions for the formation of molecular complexes and mini-starbursts. Using a sub-parsec resolution hydrodynamical simulation of a Milky Way-like galaxy, we probe these conditions to explore how and where bar (hydro-)dynamics favours the formation or destruction of molecular clouds and stars. The interplay between the kpc-scale dynamics (gas flows, shear) and the parsec-scale (turbulence) is key to this problem. We find a strong dichotomy between the leading and trailing sides of the bar, in term of cloud fragmentation and in the age distribution of the young stars. After orbiting along the bar edge, these young structures slow down at the extremities of the bar, where orbital crowding increases the probability of cloud-cloud collision. We find that such events increase the Mach number of the cloud, leading to an enhanced star formation efficiency and finally the formation of massive stellar associations, in a fashion similar to galaxy-galaxy interactions. We highlight the role of bar dynamics in decoupling young stars from the clouds in which they form, and discuss the implications on the injection of feedback into the interstellar medium, in particular in the context of galaxy formation.