An ALMA Glimpse of Dense Molecular Filaments Associated with High-mass Protostellar Systems in the Large Magellanic Cloud

Abstract

Recent millimeter/sub-millimeter facilities have revealed the physical properties of filamentary molecular clouds in relation to high-mass star formation. A uniform survey of the nearest, face-on star-forming galaxy, the Large Magellanic Cloud (LMC), complements the Galactic knowledge. We present ALMA survey data with a spatial resolution of $\sim$0.1 pc in the 0.87 mm continuum and HCO${}^{+}$(4-3) emission toward 30 protostellar objects with luminosities of 10${}^4$-10${}^{5.5}$ $L_{\odot }$ in the LMC. The spatial distributions of the HCO${}^{+}$(4-3) line and thermal dust emission are well correlated, indicating that the line effectively traces dense, filamentary gas with an H${}_2$ volume density of $\gtrsim$10${}^5$ cm${}^{-3}$ and a line mass of $\sim$10${}^3$-10${}^4$ $M_{\odot }$ pc${}^{-1}$. Furthermore, we obtain an increase in the velocity linewidths of filamentary clouds, which follows a power-law dependence on their H${}_2$ column densities with an exponent of $\sim$0.5. This trend is consistent with observations toward filamentary clouds in nearby star-forming regions withiin $\lesssim$1 kpc from us and suggests enhanced internal turbulence within the filaments owing to surrounding gas accretion. Among the 30 sources, we find that 14 are associated with hub-filamentary structures, and these complex structures predominantly appear in protostellar luminosities exceeding $\sim$5 $\times$10${}^4$ $L_{\odot }$. The hub-filament systems tend to appear in the latest stages of their natal cloud evolution, often linked to prominent H{\sc ii} regions and numerous stellar clusters. Our preliminary statistics suggest that the massive filaments accompanied by hub-type complex features may be a necessary intermediate product in forming extremely luminous high-mass stellar systems capable of ultimately dispersing the parent cloud.

21 pages, 8 figures, 4 tables, accepted for publication in ApJ