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

V. The massive filament DR21

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
e-mail: tangxindi@xao.ac.cn
² University of Chinese Academy of Sciences, 100080 Beijing, PR China
³ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 830011 Urumqi, PR China
⁴ Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, PR China
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China
⁷ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr. 1, 85748 Garching bei München, Germany
⁸ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
⁹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
¹⁰ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
¹¹ School of Mathmatics and Physics, Jinggangshan University, 343009 Ji’an, PR China
¹² School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China

Received: 26 January 2024
Accepted: 24 May 2024

Abstract

The kinetic temperature structure of the massive filament DR21 within the Cygnus X molecular cloud complex has been mapped using the IRAM 30 m telescope. This mapping employed the para-H₂CO triplet (J_KaKc = 3₀₃−2₀₂, 3₂₂−2₂₁, and 3₂₁–2₂₀) on a scale of ~0.1 pc. By modeling the averaged line ratios of para-H₂CO 3₂₂–2₂₁/3₀₃–2₀₂ and 3₂₁–2₂₀/3₀₃ –2₀₂ with RADEX under non local thermodynamic equilibrium (LTE) assumptions, the kinetic temperature of the dense gas was derived, which ranges from 24 to 114 K, with an average temperature of 48.3 ± 0.5 K at a density of n(H₂)= 10⁵ cm⁻³. In comparison to temperature measurements using NH₃ (1, 1)/(2,2) and far-infrared (FIR) wavelengths, the para-H₂CO(3–2) lines reveal significantly higher temperatures. The dense clumps in various regions appear to correlate with the notable kinetic temperature (T_kin ≳ 50 K) of the dense gas traced by H₂CO. Conversely, the outskirts of the DR21 filament display lower temperature distributions (T_kin < 50 K). Among the four dense cores (N44, N46, N48, and N54), temperature gradients are observed on a scale of ~0.1–0.3 pc. This suggests that the warm dense gas traced by H₂CO is influenced by internal star formation activity. With the exception of the dense core N54, the temperature profiles of these cores were fitted with power-law indices ranging from −0.3 to −0.5, with a mean value of approximately −0.4. This indicates that the warm dense gas probed by H₂CO is heated by radiation emitted from internally embedded protostar(s) and/or clusters. While there is no direct evidence supporting the idea that the dense gas is heated by shocks resulting from a past explosive event in the DR21 region on a scale of ~0.1 pc, our measurements of H₂CO toward the DR21W1 region provide compelling evidence that the dense gas in this specific area is indeed heated by shocks originating from the western DR21 flow. Higher temperatures as traced by H₂CO appear to be associated with turbulence on a scale of ~0.1 pc. The physical parameters of the dense gas as determined from H₂CO lines in the DR21 filament exhibit aremarkable similarity to the results obtained in OMC-1 and N113, albeit on a scale of approximately 0.1–0.4 pc. This may imply that the physical mechanisms governing the dynamics and thermodynamics of dense gas traced by H₂CO in diverse star formation regions may be dominated by common underlying principles despite variations in specific environmental conditions.