Recently, Dilda Berdikhan, a PhD student from the star formation and evolution research group of the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences (CAS), and her collaborators used the NanShan 26-meter Radio Telescope (NSRT) to observe NH3 (1,1) and (2,2) inversion transitions in the Planck cold core Milky Way.
The results have been published in Astronomy & Astrophysics.
The Planck cold cores are a set of sources identified by the Planck team in 2011 using the Planck telescope's all-sky data in the millimeter to sub-millimeter wavelength range. Subsequent observational studies have shown that these Planck sources are in early stages of star formation. Ammonia molecule is an excellent tracer of molecular clouds with a density of ~103 cm-3 and a temperature of < 40 K.
The researchers thus performed ammonia observations towards 672 Planck sources using the NSRT. The results indicated that 249 (37%) Planck cold cores detected NH3(1,1) emission lines, with 187 cores detected hyperfine structure, and 76 cores showing detections of NH3(2,2) emission lines.
They calculated important physical parameters of the cold cores, such as NH3 line width, column density, kinematic temperature, and NH3 abundance. Comparisons with samples from various evolutionary stages have revealed that NH3 kinematic temperature can serve as a tool for distinguishing between different stages. The kinematic temperature of UC HII region candidates is higher than that of Planck cold cores, while the latter exhibit lower temperatures than high infrared extinction clouds.
Additionally, the distribution of thermal and non-thermal velocities indicated that ammonia molecules can serve as ideal probes for the supersonic motion of high-density gas within Planck cold cores. The slight differences in line-of-sight velocities between NH3 and CO isotopes suggested negligible motion of the cores relative to their envelopes. Furthermore, the similar line widths between NH3 and 13CO/C18O molecules implied an early quiescent state of the Planck cold cores.
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