Abstract:We present a numerical study of the balance between the gravitational (Eg), kinetic (Ek), and magnetic (Em) energies of structures within a hub-filament system in a simulation of the formation and global hierarchical collapse (GHC) of a giant molecular cloud. For structures defined by various density thresholds, and at different evolutionary stages, we investigate the scaling of the virial parameter, α, with mass M, and of the Larson ratio, ${\cal {L}}_v\equiv \sigma _v/R^{1/2}$, with column density Σ, where σ… Show more
“…Another key difference between GHC and I2 is that GHC predicts that unbound low-mass or low-column density structures are being compressed by the infall from larger-scale bound structures (Gómez et al 2021;Camacho et al 2023). This implies that the virial parameter should decrease with increasing scale in hierarchically embedded structures.…”
Section: Comparison With Theoretical Modelsmentioning
There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+0.758 (G310 hereafter), which reveals unambiguous evidence of mass inflow from the cloud scale via the filaments onto the forming protostar(s) at the hub conforming with the model predictions. Continuum and molecular line data from the ATOMS and MALT90 surveys that cover different spatial scales are used. Three filaments (with a total mass of 5.7 ± 1.1 × 103
M
⊙) are identified converging toward the central hub region where several signposts of high-mass star formation have been observed. The hub region contains a massive clump (1280 ± 260 M
⊙) harboring a central massive core. Additionally, five outflow lobes are associated with the central massive core implying a forming cluster. The observed large-scale, smooth, and coherent velocity gradients from the cloud down to the core scale, and the signatures of infall motion seen in the central massive clump and core, clearly unveil a nearly continuous, multi-scale mass accretion/transfer process at a similar mass infall rate of ∼10−3
M
⊙ yr−1 over all scales, feeding the central forming high-mass protostar(s) in the G310 HFS cloud.
“…Another key difference between GHC and I2 is that GHC predicts that unbound low-mass or low-column density structures are being compressed by the infall from larger-scale bound structures (Gómez et al 2021;Camacho et al 2023). This implies that the virial parameter should decrease with increasing scale in hierarchically embedded structures.…”
Section: Comparison With Theoretical Modelsmentioning
There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+0.758 (G310 hereafter), which reveals unambiguous evidence of mass inflow from the cloud scale via the filaments onto the forming protostar(s) at the hub conforming with the model predictions. Continuum and molecular line data from the ATOMS and MALT90 surveys that cover different spatial scales are used. Three filaments (with a total mass of 5.7 ± 1.1 × 103
M
⊙) are identified converging toward the central hub region where several signposts of high-mass star formation have been observed. The hub region contains a massive clump (1280 ± 260 M
⊙) harboring a central massive core. Additionally, five outflow lobes are associated with the central massive core implying a forming cluster. The observed large-scale, smooth, and coherent velocity gradients from the cloud down to the core scale, and the signatures of infall motion seen in the central massive clump and core, clearly unveil a nearly continuous, multi-scale mass accretion/transfer process at a similar mass infall rate of ∼10−3
M
⊙ yr−1 over all scales, feeding the central forming high-mass protostar(s) in the G310 HFS cloud.
How molecular clouds fragment into dense structures that eventually form stars is an open question. We investigate the relative importance of gravity (both self-gravity and tidal forces) and the volume and surface terms of kinetic, thermal, and magnetic energy for the formation and evolution of molecular clouds and their sub-structures based on the SILCC-Zoom simulations. These simulations follow the self-consistent formation of cold molecular clouds down to scales of 0.1 pc from the diffuse supernova-driven interstellar medium in a stratified galactic disc. We study the time evolution of seven molecular clouds (of which five are magnetized) over ∼2 Myr. Using a dendrogram, we identify hierarchical 3D sub-structures inside the clouds with the aim of understanding their dynamics. The virial analysis shows that the dense gas is indeed dominated by the interplay of gravity and turbulence, while magnetic fields and thermal pressure are mostly important for fluffy, atomic structures. However, not all bound structures are gravitationally bound; some are held together by ram pressure aided by other surface terms. Overall, ∼36% of the clouds have >50% of their mass in ”potentially gravity bound” structures. A subset of them (70%) is “potentially bound” by gravity on scales >15 pc. A detailed tidal analysis shows that the tidal tensor is highly anisotropic. Yet the tidal forces are generally not strong enough to disrupt either large-scale or dense sub-structures but cause their deformation. When comparing the tidal and crossing time scales, we find that tidal forces do not appear to be the main driver of turbulence within the molecular clouds.
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