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

Abstract

Recent millimeter/submillimeter 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 ∼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 _⊙ 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 ≳10 ^5 cm ^−3 and a line mass of ∼10 ^3 –10 ^4 M _⊙ pc ^−1 . Furthermore, we obtain an increase in the velocity line widths of filamentary clouds, which follows a power-law dependence on their H _2 column densities with an exponent of ∼0.5. This trend is consistent with observations toward filamentary clouds in nearby star-forming regions within ≲1 kpc from us and suggests enhanced internal turbulence within the filaments due 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 ∼5 × 10 ^4 L _⊙ . The hub-filament systems tend to appear in the latest stages of their natal cloud evolution, often linked to prominent H 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.

Keywords

• Star formation
• Protostars
• Molecular clouds
• Interstellar medium
• Large Magellanic Cloud
• Local Group