Contributed Talk - Splinter Computation

Thursday, 24 September 2020, 11:17   (virtual room B)

SILCC-zoom: gravo-turbulence or global hierarchical collapse?

S. Ganguly, S. Walch, S. D. Clarke, D. Seifried
University of Cologne

How molecular clouds fragment and create the dense structures which go on to form stars is an open question. We consider different scenarios that have been put forward: (1) the gravo-turbulent scenario in which turbulence plays the dominant role in the fragmentation and gravity is only important in the densest structures; (2) the global hierarchical collapse scenario in which gravity is dominant on all scales and turbulence is driven by gravitational collapse. We present a numerical study of cloud fragmentation and structure formation using the SILCC-Zoom simulations (Seifried+2017). These simulations follow the self-consistent formation of molecular clouds in a few hundred pc sized region of a stratified galactic disc; and include self-gravity, magnetic fields, supernova driven turbulence, as well as a non-equilibrium chemical network. We study the time evolution of seven molecular clouds (five with magnetic fields and two without) for 1.5 Myr with a maximum resolution of 0.1 pc. Using a dendrogram we identify hierarchical structures with $ ho_{min}$ > $10^{-22}$ gm/cc which form within the clouds, and classify their morphology as spheroidal, filamentary or sheet-like. We find that six out of seven clouds are sheet-like on the largest scales with filamentary structures embedded within, which is consistent with the bubble driven molecular cloud formation mechanism proposed by Inutsuka+2015. We further analyse the energetics (self-gravity, turbulent support, thermal energy, magnetic energy and ram pressure) and chemical abundances of these structures over time. We find that: (1) our simulated clouds are roughly virialized on the large (>10 pc) scales; (2) on scales of up to a few pc, the densest structures are dominated by self-gravity while the rest are kinetically dominated; (3) the atomic structures have less potential energy and have energetically different behaviour to the molecular structures; (4) this behaviour does not significantly alter over the time period we analyse; and (5) six out of seven clouds show some global inflow signature, which could indicate shock compression or global collapse as the origin.