Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC

Abstract

We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used ∼1 . 6 (∼0.4 pc) resolution measurements of the para-H 2 CO J KaKc = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 transitions near 218.5 GHz to constrain RADEX non-LTE models of the physical conditions. The gas kinetic temperatures derived from the para-H 2 CO line ratios 3 22 -2 21 /3 03 -2 02 and 3 21 -2 20 /3 03 -2 02 range from 28 to 105 K in N113 and 29 to 68 K in N159W. Distributions of the dense gas traced by para-H 2 CO agree with those of the 1.3 mm dust and Spitzer 8.0 µm emission, but do not significantly correlate with the Hα emission. The high kinetic temperatures (T kin 50 K) of the dense gas traced by para-H 2 CO appear to be correlated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The lower temperatures (T kin < 50 K) are measured at the outskirts of the H 2 CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H 2 CO are weakly affected by the external sources of the Hα emission. The non-thermal velocity dispersions of para-H 2 CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H 2 CO is related to turbulence on a ∼0.4 pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.