Star formation in shells of colliding multi-SNe bubbles

Abstract

It is believed that when bubbles formed by multiple supernovae explosions interact with one another, they stimulate star formation in overlapping shells. We consider the evolution of a shocked layer formed by the collision of two identical bubbles each of which originated from OB clusters of ∼ 50 members and ∼ 50 pc. The clusters are separated by 200-400 pc. We found that depending on evolutionary status of colliding bubbles the shocked layer can either be destroyed into diffuse lumps, or be fragmented into dense clumps: the former occurs in collisions of young bubbles with continuing supernovae explosions, and the latter occurs in older bubble interactions. We argue that fragmentation efficiency in shells depends on external heating: for a heating rate < ∼ 1.7×10 −24 erg s −1 the number of fragments formed in a collision of two old bubbles reaches several tens at t ∼ 4 Myr, while a heating rate > ∼ 7 × 10 −24 erg s −1 prevents fragmentation. The clumps formed in freely expanding parts of bubbles are gradually destroyed and disappear on t < ∼ 1 Myr, whereas those formed in the overlapping shells survive much longer. Because of this the number of fragments in an isolated bubble begins to decrease after reaching a maximum, while in collision of two old bubbles it fluctuates around 60-70 until longer than t ∼ 5 Myr.

Star formation complexes in the ‘galaxy-sized’ supergiant shell of the galaxy HolmbergI

“…Another well known mechanism of triggering of star formation is the collision of several expanding supershells. It was reproduced in numerical and analytical models by different authors (e.g., Chernin et al 1995;Ntormousi et al 2011;Kawata et al 2014;Vasiliev & Shchekinov 2017) and observed in a number of nearby galaxies (e.g. Lozinskaya 2002;Egorov et al 2017).…”

“…In Egorov et al (2017), we showed that star formation on the rims of an SGS can often be a result of its collision with other neighbouring H i SGSs. The existing models of collided superbubbles also support this possibility (e.g., Chernin et al Moustakas et al (2010) 1995; Ntormousi et al 2011;Kawata et al 2014;Vasiliev & Shchekinov 2017).…”