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Studying the driving modes of turbulence is important for characterizing theimpact of turbulence in various astrophysical environments. The driving mode ofturbulence is parameterized by $b$, which relates the width of the gas densityPDF to the turbulent Mach number; $b\approx 1/3$, $1$, and $0.4$ correspond todriving that is solenoidal, compressive, and a natural mixture of the two,respectively. In this work, we use high-resolution (sub-pc) ALMA $^{12}$CO ($J$= $2-1$), $^{13}$CO ($J$ = $2-1$), and C$^{18}$O ($J$ = $2-1$) observations offilamentary molecular clouds in the star-forming region N159E (the PapillonNebula) in the Large Magellanic Cloud (LMC) to provide the first measurement ofturbulence driving parameter in an extragalactic region. We use a non-localthermodynamic equilibrium (NLTE) analysis of the CO isotopologues to constructa gas density PDF, which we find to be largely log-normal in shape with someintermittent features indicating deviations from lognormality. We find that thewidth of the log-normal part of the density PDF is comparable to the supersonicturbulent Mach number, resulting in $b \approx 0.9$. This implies that thedriving mode of turbulence in N159E is primarily compressive. We speculate thatthe compressive turbulence could have been powered by gravo-turbulentfragmentation of the molecular gas, or due to compression powered by H I flowsthat led to the development of the molecular filaments observed by ALMA in theregion. Our analysis can be easily applied to study the nature of turbulencedriving in resolved star-forming regions in the local as well as thehigh-redshift Universe.

monthly notices of the royal astronomical society

First extragalactic measurement of the turbulence driving parameter:  ALMA observations of the star-forming region N159E in the Large Magellanic  Cloud