Large-scale periodic velocity oscillation in the filamentary cloud G350.54+0.69

Liu, Hongli; Stutz, Amelia M.; Yuan, Jinghua

doi:10.1093/mnras/stz1340

Cited by 40 publications

(39 citation statements)

References 55 publications

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“…These factors give us confidence that the correlated periodicity between density and velocity is not simply an artefact of the fact that our spectral decomposition only probes observational estimators of the true underlying density and velocity fields. Similar features observed in both low-mass 118,129 and high-mass 130 filaments, using independent tracers of gas column-density and centroid velocity (see also the CMZ data presented in this work), instead points to a dynamical origin of the velocity oscillations, strengthening our argument that such motions may be a common feature of the molecular ISM on all scales (Figure 1).…”

Section: Origins Of the Periodic Velocity Fluctuationssupporting

confidence: 83%

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

et al. 2020

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The density structure of the interstellar medium (ISM) determines where stars form and release energy, momentum, and heavy elements, driving galaxy evolution. [1][2][3][4] Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scale and galactic environment. 5 Although dense star-forming gas likely emerges from a combination of instabilities, 6, 7 convergent flows, 8 and turbulence, 9 establishing the precise origin is challenging because it requires quantifying gas motion over many orders of magnitude in spatial scale. Here we measure [10][11][12] the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span an unprecedented spatial dynamic range (10 −1 −10 3 pc). We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from 0.3−400 pc. These flows are coupled to regularly-spaced density enhancements that likely form via gravitational instabilities. 13,14 We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows. 9 Our results demonstrate that ISM structure cannot be considered in isolation. Instead, its formation and evolution is controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.We use observations that trace molecular gas in a variety of galactic environments and span a wide range of spatial scales. We measure the position-position-velocity (p-p-v) structure of the molecular ISM from 0.1 pc scales, relevant for individual star-forming cores, up to the scales of individual giant molecular clouds (GMCs), now accessible in nearby galaxies using facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA). On large (from 100 pc to >1000 pc) scales, we analyse observations of nearby galaxy NGC 4321 from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS-ALMA) survey. At intermediate (from 1 pc to 100 pc) scales, we target both the Galactic disc and the Central Molecular Zone (CMZ, i.e. the central 500 pc) of the Milky Way with data from the Galactic Ring Survey 15 and the Mopra CMZ survey, 16 respectively. On small scales (from 0.1 pc to around 10 pc) we include observations of two dense molecular clouds, G035.39-00.33 17 in the Galactic disc and G0.253+0.016 11 in the CMZ.We extract the kinematics of the gas using spectral decomposition, modelling each spectrum as a set of individual Gaussian emission features. [10][11][12] Spectral decomposition is advantageous because it yields a description of all prominent emission features observed in spectroscopic data. We visualise the results using the peak intensities and velocity centroids of the modelled emission features (Figure 1). This method facilitates the detection of small fluctuations in velocity, which can o...

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Section: Origins Of the Periodic Velocity Fluctuationssupporting

confidence: 83%

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

et al. 2020

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“…In our simulations, the velocity range reduces over time as the amplitudes of the oscillation reduce due to the sheet reaching the potential minimum. Our model and the observations of Liu et al (2019) are therefore compatible.…”

Section: Integralssupporting

confidence: 86%

“…Further work to investigate this is required. Interestingly, Liu et al (2019) investigate the internal gas kinematics of the filamentary cloud G350.54+0.69 and find a large-scale periodic velocity oscillation along the filament, with a wavelength of 1.3 pc and an amplitude of ∼0.12 km s −1 . The authors conjecture the periodic velocity oscillation could be driven by a combination of longitudinal gravitational instability and a large-scale periodic physical oscillation along the filament, possibly an example of an MHD transverse wave.…”

Section: Integralsmentioning

confidence: 99%

Striations, integrals, hourglasses, and collapse – thermal instability driven magnetic simulations of molecular clouds

Wareing

Pittard

Falle

2020

Monthly Notices of the Royal Astronomical Society

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The MHD version of the adaptive mesh refinement (AMR) code, MG, has been employed to study the interaction of thermal instability, magnetic fields and gravity through 3D simulations of the formation of collapsing cold clumps on the scale of a few parsecs, inside a larger molecular cloud. The diffuse atomic initial condition consists of a stationary, thermally unstable, spherical cloud in pressure equilibrium with lower density surroundings and threaded by a uniform magnetic field. This cloud was seeded with 10% density perturbations at the finest initial grid level around n=1.1 cm−3 and evolved with self-gravity included from the outset. Several cloud diameters were considered (100 pc, 200 pc and 400 pc) equating to several cloud masses (17,000 M⊙, 136,000 M⊙ and 1.1 × 106 M⊙). Low-density magnetic-field-aligned striations were observed as the clouds collapse along the field lines into disc-like structures. The induced flow along field lines leads to oscillations of the sheet about the gravitational minimum and an integral-shaped appearance. When magnetically supercritical, the clouds then collapse and generate hourglass magnetic field configurations with strongly intensified magnetic fields, reproducing observational behaviour. Resimulation of a region of the highest mass cloud at higher resolution forms gravitationally-bound collapsing clumps within the sheet that contain clump-frame supersonic (M ∼ 5) and super-Alfvénic (MA ∼ 4) velocities. Observationally realistic density and velocity power spectra of the cloud and densest clump are obtained. Future work will use these realistic initial conditions to study individual star and cluster feedback.

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“…Following Eq. 2 of Liu, Stutz, & Yuan (2019), the total velocity dispersion, σtot, was calculated as σ 2 tot = σ 2 th + σ 2 nt , to include both thermal and non-thermal support against gravity. In this calculation, the same temperatures as assumed for calculating core masses were taken to be the kinetic temperature of the cores, while the line widths, ∆V H 13 CO + , derived from the spectrum of H 13 CO + (1-0) averaged over each core (see Table 1) were used for the σnt estimate.…”

Section: Virial Analysismentioning

confidence: 99%

“…3.2), and thus more representative of the initial turbulence of the cloud than the line widths found in the relatively strong-feedback areas. Following Liu, Stutz, & Yuan (2019), σ th is estimated from the gas kinetic temperature and σnt is determined from ∆ V H 13 CO + . Finally, using the cloud-average density, n cl ∼ 2.6 × 10 5 cm −3 (i.e., ρ cl eff ∼ 4.4 × 10 −19 g cm −3 ) both thermal and turbulent Jeans parameters are calculated on the cloud scale.…”

Section: Jeans Length and Jeans Massmentioning

confidence: 99%

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – V. Hierarchical fragmentation and gas dynamics in IRDC G034.43+00.24

Liu

Tej

Issac

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present new 3 mm continuum and molecular lines observations from the ATOMS survey towards the massive protostellar clump, MM1, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observed are the tracers of either dense gas (e.g. HCO+/H13CO+ J=1–0) or outflows (e.g. CS J=2–1). The most complete picture to date of seven cores in MM1 is revealed by dust continuum emission. These cores are found to be gravitationally bound, with virial parameter, αvir < 2. At least four outflows are identified in MM1 with a total outflowing mass of ∼45 M⊙, and a total energy of 1 × 1047 ergs, typical of outflows from a B0-type star. Evidence of hierarchical fragmentation, where turbulence dominates over thermal pressure, is observed at both the cloud and the clump scales. This could be linked to the scale-dependent, dynamical mass inflow/accretion on clump and core scales. We therefore suggest that the G34 cloud could be undergoing a dynamical mass inflow/accretion process linked to the multi-scale fragmentation, which leads to the sequential formation of fragments of the initial cloud, clumps, and ultimately dense cores, the sites of star formation.

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Large-scale periodic velocity oscillation in the filamentary cloud G350.54+0.69

Cited by 40 publications

References 55 publications

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

Striations, integrals, hourglasses, and collapse – thermal instability driven magnetic simulations of molecular clouds

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – V. Hierarchical fragmentation and gas dynamics in IRDC G034.43+00.24

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