IC 5146 Dark Streamer: The First Reliable Candidate of Edge Collapse, Hub-filament Systems, and Intertwined Sub-filaments

A simple Gaussian size deconvolution method is routinely used to remove the blur of observed images caused by insufficient angular resolutions of existing telescopes, thereby to estimate the physical sizes of extracted sources and filaments. To ensure that the physical conclusions derived from observations are correct, it is necessary to know the inaccuracies and biases of the size deconvolution method, which is expected to work when the structures, as well as the telescope beams, have Gaussian shapes. This study employed model images of the spherical and cylindrical objects with Gaussian and power-law shapes, representing the dense cores and filaments observed in star-forming regions. The images were convolved to a wide range of angular resolutions to probe various degrees of resolvedness of the model objects. Simplified shapes of the flat, convex, and concave backgrounds were added to the model images, then planar backgrounds across the footprints of the structures are subtracted and sizes of the sources and filaments were measured and deconvolved. When background subtraction happens to be inaccurate, the observed structures acquire profoundly non-Gaussian profiles. The deconvolved half maximum sizes can be strongly under- or overestimated, by factors of up to ~20 when the structures are unresolved or partially resolved. For resolved structures, the errors are generally within a factor of ~2; although, the deconvolved sizes can be overestimated by factors of up to ~6 for some power-law models. The results show that Gaussian size deconvolution cannot be applied to unresolved structures, whereas it can only be applied to the Gaussian-like structures, including the critical Bonnor-Ebert spheres, when they are at least partially resolved. The deconvolution method must be considered inapplicable for the power-law sources and filaments with shallow profiles. This work also reveals subtle properties of convolution for structures of different geometry. When convolved with different kernels, spherical objects and cylindrical filaments with identical profiles obtain different widths and shapes. In principle, a physical filament, imaged by the telescope with a non-Gaussian point-spread function, could appear substantially shallower than the structure is in reality, even when it is resolved.

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Fragmentation and dynamics of dense gas structures in the proximity of massive young stellar object W42-MME

Bhadari,

Dewangan,

Pirogov

et al. 2023

Monthly Notices of the Royal Astronomical Society

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We present an analysis of the dense gas structures in the immediate surroundings of the massive young stellar object (MYSO) W42-MME, using the high-resolution (0″.31 × 0″.25) Atacama Large Millimetre/submillimetre Array dust continuum and molecular line data. We performed a dendrogram analysis of H13CO+ (4–3) line data to study multiscale structures and their spatio–kinematic properties, and analysed the fragmentation and dynamics of dense structures down to ∼2000 au scale. Our results reveal 19 dense gas structures, out of which 12 are leaves and 7 are branches in dendrogram terminology. These structures exhibit transonic–supersonic gas motions (1$\lt \mathcal {M}\lt 5$) with overvirial states (αvir ≥ 2). The non-thermal velocity dispersion–size relation (σnt–L) of dendrogram structures shows a weak negative correlation, while the velocity dispersion across the sky ($\delta \mathit {V_{\rm lsr}}$) correlates positively with structure size (L). Velocity structure function (S2(l)1/2) analysis of H13CO+ data reveals strong power-law dependences with lag (l) up to a scale length of ≲6000 au. The mass–size (M–R) relation of dendrogram structures shows a positive correlation with power-law index of 1.73 ± 0.23, and the leaf L17 hosting W42-MME meets the mass–size conditions for massive star formation. Blue asymmetry is observed in the H12CO+ (4–3) line profiles of most of the leaves, indicating infall. Overall, our results observationally support the hierarchical and chaotic collapse scenario in the proximity of the MYSO W42-MME.

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IC 5146 Dark Streamer: The First Reliable Candidate of Edge Collapse, Hub-filament Systems, and Intertwined Sub-filaments

Cited by 4 publications

References 72 publications

Turbulence and magnetic fields in star formation

Turbulence and magnetic fields in star formation

Inaccuracies and biases of the Gaussian size deconvolution for extracted sources and filaments

Fragmentation and dynamics of dense gas structures in the proximity of massive young stellar object W42-MME

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