The Impact of Stellar Radiative Feedback on Formation of Young Massive Clusters via Fast HI Gas Collisions

TL;DR

This study uses 3D magnetohydrodynamics simulations to explore how fast HI gas collisions can form massive, compact gas clumps that survive stellar feedback and evolve into young massive clusters, shedding light on their formation mechanisms.

Contribution

It demonstrates that high-velocity HI gas collisions can produce massive, dense gas clumps capable of becoming YMCs despite ionization feedback, a novel insight into cluster formation processes.

Findings

Massive gas clumps (~10^5 M_sun) with ~5 pc size form via fast HI collisions.

Clumps have high escape velocities, enabling gas retention against ionization feedback.

Star formation within these clumps can lead to YMCs despite feedback effects.

Abstract

Young massive clusters (YMCs) are dense aggregates of young stars and are often speculated as potential precursors to globular clusters. However, the formation mechanism of massive and compact gas clumps that precede YMCs remains unknown. In this paper, we study the formation of such massive clumps via fast HI gas collisions (~100 km/s) as suggested by recent observations and their subsequent evolution into YMCs by using three-dimensional magnetohydrodynamics simulations involving self-gravity and detailed thermal/chemical processes. In particular, the impact of ionization feedback from stellar radiation is included in an approximate fashion where the temperature within the HII regions is elevated to 10,000 K, while supernova feedback is not included. We examine whether the resulting massive clumps can survive this ionization feedback and evolve into YMCs. Our simulations reveal the emergence of gas clumps that do not only possess substantial mass (~10^5 M_sun) but also sufficient compactness (~5 pc). Notably, these clumps exhibit significantly higher escape velocities compared to the sound speed of the HII region, indicating effective gravitational retention of gas against feedback-induced evaporation. Consequently, these conditions foster efficient star formation within the massive gas clumps, ultimately leading to their evolution into YMCs. We also perform simulations involving lower-velocity gas collisions, approximately 15 km/s, typical shock velocities induced by galactic superbubbles.