Edge collapse and subsequent longitudinal accretion in Filament S242

Abstract

Filament S242 is 25 pc long with massive clumps and YSO clusters concentrated in its end regions; it is considered a good example of edge collapse. We mapped this filament in the ${}^{12}$CO(1-0) and ${}^{13}$CO(1-0) lines. A large-scale velocity gradient along filament S242 has been detected; the relative velocity between the two end-clumps is $\sim$ 3 km s${}^{-1}$, indicating an approaching motion between them. These signatures are consistent with the filament S242 being formed through the collapse of a single elongated entity, where an effect known as "gravitational focusing" drives the ends of the filament to collapse (edge collapse). Based on this picture, we estimate a collapse timescale of $\sim$ 4.2 Myr, which is the time needed for a finite and elongated entity evolving to the observed filament S242. For the whole filament, we find that increases in surface densities lead to increases in velocity dispersion, which can be consistently explained as the result of self-gravity. We also calculated the contribution of longitudinal collapse to the observed velocity dispersion and found it to be the dominant effect in driving the gas motion near the end-clumps. We propose that our filament S242 is formed through a two-stage collapse model, where the edge collapse of a truncated filament is followed by a stage of longitudinal accretion toward the dense end-clumps.

14 pages, 11 figures; Accepted for publication in A&A

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• Molecular Gas Structures traced by ${}^{13}$CO Emission in the 18,190 ${}^{12}$CO Molecular Clouds from the MWISP Survey
• IC 5146 dark Streamer: is a first reliable candidate of edge collapse, hub-filament systems, and intertwined sub-filaments?
• Bimodal orientation distribution and head-tail asymmetry of a sample of filamentary molecular clouds
• ArTéMiS imaging of the filamentary infrared dark clouds G1.75-0.08 and G11.36+0.80: Dust-based physical properties of the clouds and their clumps