Ammonia observations of Planck cold cores^★

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
e-mail: dilda@xao.ac.cn; jarken@xao.ac.cn; 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, Nanjing, JiangSu 210008, 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 Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁷ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
⁸ Energetic Cosmos Laboratory, Nazarbayev University, Astana 010000, Kazakhstan
⁹ Institute of Experimental and Theoretical Physics, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan

Received: 23 October 2023
Accepted: 30 January 2024

Abstract

Single-pointing observations of NH₃ (1,1) and (2,2) were conducted toward 672 Planck Early Cold Cores (ECCs) using the Nanshan 26-m radio telescope. Out of these sources, a detection rate of 37% (249 cores) was achieved, with a NH₃ (1,1) hyperfine structure detected in 187 cores and NH₃ (2,2) emission lines detected in 76 of them. The detection rate of NH₃ is positively correlated with the continuum emission fluxes at a frequency of 857 GHz. Among the observed 672 cores, ~22% have associated stellar and infrared objects within the beam size (~2′). This suggests that most of the cores in our sample may be starless. The kinetic temperatures of the cores range from 8.9 to 20.7 K, with an average of 12.3 K, indicating a coupling between gas and dust temperatures. The ammonia column densities range from 3.6 × 10¹⁴ to 6.07 × 10¹⁵ cm⁻², with a median value of 2.04 × 10¹⁵ cm⁻². The fractional abundances of ammonia range from 0.3 to 9.7 × 10⁻⁷, with an average of 2.7 × 10⁻⁷, which is one order of magnitude larger than that of massive star-forming (MSF) regions and infrared dark clouds (IRDCs). The correlation between thermal and nonthermal velocity dispersion of the NH₃ (1,1) inversion transition indicates the dominance of supersonic nonthermal motions in the dense gas traced by NH₃, and the relationship between these two parameters in Planck cold cores is weaker, with lower values observed for both parameters relative to other samples under our examination. The cumulative distribution shapes of line widths in the Planck cold cores closely resemble those of the dense cores found in regions of Cepheus, in addition to Orion L1630 and L1641, with higher values compared to Ophiuchus.