Supernova Driving. I. The Origin of Molecular Cloud Turbulence

Abstract

Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by supernova (SN) explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SNdriven turbulence in a volume of (250 pc) 3 , specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interiors of MCs, and that the velocity-size relation of the MCs selected from our simulation is consistent with that of MCs from the OuterGalaxy Survey, the largest MC sample available. The mass-size relation and the mass and size probability distributions also compare successfully with those of the Outer Galaxy Survey. Finally, we show that MC turbulence is super-Alfvénic with respect to both the mean and rms magnetic-field strength. We conclude that MC structure and dynamics are the natural result of SN-driven turbulence.

Structure distribution and turbulence in self-consistently supernova-driven ISM of multiphase magnetized galactic discs

“…These results are different from the work of Padoan et al (2016) since they find that the solenoidal modes dominate while we find that this depends on altitude but in the equatorial plane the compressible modes are dominating. One major difference with this work is the stratification induced by the galactic gravitational field.…”

“…Kritsuk et al 2007;Federrath & Klessen 2012;Federrath 2013), the turbulence in our simulation is supernova-driven, and energy is likely injected at scales on the order of 50 pc although since supernovae are correlated, they may also inject energy at larger scales. This work (Iffrig & Hennebelle 2015b, and this paper) shows similarities to the work by Padoan et al (2016), but differs from it in the following respects: i) their 250 pc box does not include vertical stratification and is periodic; ii) in their study the supernovae are not correlated to star-forming regions; iii) their resolution is not uniform (128 3 base grid). This will introduce some discrepancies that will be discussed.…”

“…In this latter case, an energy power spectrum k −8/3 would be expected. Let us stress that the enstrophy cascade that would lead to kF 2 ∝ k −3 requires conservation of the vorticity which is not ensured in the magnetized and non-barotropic flows like the ISM (Hennebelle & Audit 2007;Padoan et al 2016). …”

“…Due to technical difficulties, in particular the very small time steps induced by the high velocities and temperatures that feedback generates, these studies are usually limited to relatively modest numerical spatial resolution and as a consequence the detailed flow properties have been more rarely considered (de Avillez & Breitschwerdt 2007;Padoan et al 2016), being mainly addressed through smaller scale simulations in which the energy input has to be prescribed (Vázquez-Semadeni et al 2006;Kritsuk et al 2007;Banerjee et al 2009;Audit & Hennebelle 2010;Inoue & Inutsuka 2012).…”

Galactic supernova remnant candidates discovered by THOR

“…Tammann et al, 1994), and therefore the number of SNRs in the Galaxy is tied to recent massive star formation activity. SN inject energy into the interstellar medium (ISM), driving molecular cloud turbulence and galactic fountains out of the disk (de Avillez & Breitschwerdt, 2005;Joung et al, 2009;Padoan et al, 2016;Girichidis et al, 2016). This feedback can determine the disk scale height and star formation properties of a galaxy (Ostriker et al, 2010;Ostriker & Shetty, 2011;FaucherGiguère et al, 2013).…”