The Size Distribution of Superbubbles in the Interstellar Medium

Summary

We use the standard, adiabatic shell evolution to predict the size distribution N(R) for populations of SN-driven superbubbles in a uniform ISM. We derive N(R) for simple cases of superbubble creation rate and mechanical luminosity function. We then compare our predictions for N(R) with the largely complete HI hole catalogue for the SMC, with a view toward the global structure of the ISM in that galaxy. We also present a preliminary derivation for N(v), the distribution of shell expansion velocities.

Introduction

Core-collapse supernovae (SNe) tend to be correlated in both space and time because of the clustering of the massive (≳ 8M_⊙) star progenitors. These clustered SNe, along with stellar winds of the most massive stars, produce superbubble structures in both the warm ionized (10⁴ K) and atomic H I components of the interstellar medium (ISM) in star-forming galaxies. The hot, coronal component of the ISM is thought to originate largely from the shock heating of material interior to shells of superbubbles and supernova remnants (SNRs). Total kinetic energies deposited into the interstellar environment are in the range 10⁵¹ − 10⁵⁴ erg for OB associations, and ≳ 10⁵⁵ erg for starburst phenomena. Hence, the large-scale structure and kinematics of the multi-phase ISM could be largely determined by this superbubble activity. Likewise, this effect should influence turbulence on global, macroscopic scales, which then cascades to smaller scales.