Is Molecular Cloud Turbulence Driven by External Supernova Explosions?

Abstract

We present high-resolution (∼ 0.1 pc), hydrodynamical and magnetohydrodynamical simulations to investigate whether the observed level of molecular cloud (MC) turbulence can be generated and maintained by external supernova (SN) explosions. The MCs are formed self-consistently within their large-scale galactic environment following the non-equilibrium formation of H 2 and CO including (self-) shielding and important heating and cooling processes. The MCs inherit their initial level of turbulence from the diffuse ISM, where turbulence is injected by SN explosions. However, by systematically exploring the effect of individual SNe going off outside the clouds, we show that at later stages the importance of SN-driven turbulence is decreased significantly. This holds for different MC masses as well as for MCs with and without magnetic fields. The SN impact also decreases rapidly with larger distances. Nearby SNe (d ∼ 25 pc) boost the turbulent velocity dispersions of the MC by up to 70 per cent (up to a few km s −1 ). For d > 50 pc, however, their impact decreases fast with increasing d and is almost negligible. For all probed distances the gain in velocity dispersion decays rapidly within a few 100 kyr. This is significantly shorter than the average timescale for an MC to be hit by a nearby SN under solar neighbourhood conditions (∼ 2 Myr). Hence, at these conditions SNe are not able to sustain the observed level of MC turbulence. However, in environments with high gas surface densities and SN rates ,like the Central Molecular Zone, observed elevated MC dispersions could be triggered by external SNe.

On estimating angular momenta of infalling protostellar cores from observations

“…In our simulations, while there is an initial turbulent velocity field which seeds structure, at the later stages where we observe our cores, complex gravitational accelerations produced by the non-uniform density fluctuations and sinks are driving the motions. This scenario is consistent with the results of Seifried et al (2018), who performed large-scale numerical simulations of molecular clouds created and perturbed by external supernovae. Seifried et al found that the initial turbulence created during cloud formation decays rapidly as the cloud becomes more massive, concluding that SNe are generally not able to sustain observed molecular cloud turbulence.…”

The Cloud Factory II: gravoturbulent kinematics of resolved molecular clouds in a galactic potential

“…Onsager 1949), which, on small scales, rapidly lose energy via viscous dissipation. Also, this indicates that in these complexes, driving of large-scale velocity fluctuations by random supernovae is unable to maintain the level of turbulence within the clouds (see also Ibáñez-Mejía et al 2017 andSeifried et al 2018 who find similar results). Turning on self-gravity dramatically changes this behaviour.…”

Can magnetized turbulence set the mass scale of stars?

“…However, their effect upon the IMF must be indirect, because they occur too late to significantly affect the evolution of dense clumps in which star clusters form. Their main role in star formation is likely maintaining the state of ISM turbulence on the scale of the galactic scale height and driving galactic outflows (via super-bubbles and chimneys), thus regulating the ISM gas densities and other "environmental" properties which set the properties of GMCs in turn (e.g., Hopkins et al 2011Hopkins et al , 2012Walch et al 2015;Padoan et al 2017;Seifried et al 2018;Guszejnov et al 2020).…”