Bubble structures are ubiquitously observed in the interstellar medium from the vicinity of the Solar system to nearby star-forming galaxies. Such bubbles, presumably created by HII regions, supernovae (SNe), and superbubbles, influence the dynamical and thermal evolution of surrounding molecular clouds (MCs). Previous numerical studies suggest that MCs cannot maintain their observed level of supersonic turbulence more than 1 Myr if influenced by only a single SN. However, the typical lifetime of MCs (a few 10 Myr) is long enough to experience many compressions by multiple SNe and thus the long-term cloud evolution (> 1 Myr) with multiple SNe remains to be investigated.
We performed zoomed simulations on a 100 pc scale toward a MC in our simulations of a stratified galactic disk (SILCC project). We systematically injected additional SNe in the vicinity of the targeted cloud by varying the frequency and spatial clustering of SNe.
Our results show that the impact by six SNe occurred at 25 pc distance from the cloud enhance turbulence to > 10 km/s on 1 - 100 pc scale longer than 1 Myr. Such enhancement is prominent in lower density volumes, while regions with a high total column density (> 10^22 cm-2) do not experience significant turbulent enhancement.
To discuss the observability of multiple SN impact, we also performed synthetic observations in H alpha by using MAPPINGS V and in 12CO(J=1-0) by using RADMC-3D. Out results suggest that H alpha captures the expanding motion of hot supernova remnant bubbles and the subsequent turbulence. Meanwhile, 12CO(J=1-0) tends to trace only the periphery of expanding bubbles. The velocity dispersion measured in 12CO(J=1-0) amounts to 25 percent of the total turbulent energy even when six SNe occurred. Therefore, multi-band observations are ideal to evaluate the impact by multiple SNe. Mid-J and high-J CO transitions will become interesting lines to bridge between radio and optical lines.