Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

IV. The ALMA view of N113 and N159W in the LMC^★

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
e-mail: tangxindi@xao.ac.cn
² Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 830011 Urumqi, PR China
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: chenkel@mpifr-bonn.mpg.de
⁴ Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁵ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea
⁶ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁷ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China
⁸ Argelander Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁹ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
¹⁰ Observatorio de Madrid, OAN-IGN, Alfonso XII, 3, 28014- Madrid, Spain
¹¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355, Chile
¹² Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355, Chile
¹³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁴ Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
¹⁵ Ioffe Physical-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia
¹⁶ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
¹⁷ National Radio Astronomy Observatory, PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA
¹⁸ Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹⁹ Department of Physics, Nagoya University, Furo-cho, Chikusa-ku Nagoya, 464-8601, Japan
²⁰ School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China
²¹ University of Chinese Academy of Sciences, 100080 Beijing, PR China

Received: 16 July 2021
Accepted: 23 August 2021

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-H₂CO J_KaKc = 3₀₃–2₀₂, 3₂₂–2₂₁, and 3₂₁–2₂₀ transitions near 218.5 GHz to constrain RADEX non local thermodynamic equilibrium models of the physical conditions. The gas kinetic temperatures derived from the para-H₂CO line ratios 3₂₂–2₂₁/3₀₃–2₀₂ and 3₂₁–2₂₀/3₀₃–2₀₂ range from 28 to 105 K in N113 and 29 to 68 K in N159W. Distributions of the dense gas traced by para-H₂CO agree with those of the 1.3 mm dust and Spitzer 8.0 μm emission, but they do not significantly correlate with the Hα emission. The high kinetic temperatures (T_kin ≳ 50 K) of the dense gas traced by para-H₂CO appear to be correlated with the embedded infrared sources inside the clouds and/or young stellar objects in the N113 and N159W regions. The lower temperatures (T_kin < 50 K) were measured at the outskirts of the H₂CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H₂CO are weakly affected by the external sources of the Hα emission. The non thermal velocity dispersions of para-H₂CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H₂CO 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.