Ammonia observations towards the Aquila Rift cloud complex

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
e-mail: 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, 830011 Urumqi, PR China
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: chenkel@mpifr-bonn.mpg.de
⁵ Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁶ Department of Solid State Physics and Nonlinear Physics, Faculty of Physics and Technology, AL-Farabi Kazakh National University, 050040 Almaty, Kazakhstan

Received: 4 February 2020
Accepted: 23 September 2020

Abstract

We surveyed the Aquila Rift complex including the Serpens South and W 40 regions in the NH₃ (1,1) and (2,2) transitions making use of the Nanshan 26-m telescope. Our observations cover an area of ~ 1.5° × 2.2° (11.4 pc × 16.7 pc). The kinetic temperatures of the dense gas in the Aquila Rift complex obtained from NH₃ (2,2)/(1,1) ratios range from 8.9 to 35.0 K with an average of 15.3 ± 6.1 K (errors are standard deviations of the mean). Low gas temperatures are associated with Serpens South ranging from 8.9 to 16.8 K with an average of 12.3 ± 1.7 K, while dense gas in the W 40 region shows higher temperatures ranging from 17.7 to 35.0 K with an average of 25.1 ± 4.9 K. A comparison of kinetic temperatures derived from para-NH₃ (2,2)/(1,1) against HiGal dust temperatures indicates that the gas and dust temperatures are in agreement in the low-mass-star formation region of Serpens South. In the high-mass-star formation region W 40, the measured gas kinetic temperatures are higher than those of the dust. The turbulent component of the velocity dispersion of NH₃ (1,1) is found to be positively correlated with the gas kinetic temperature, which indicates that the dense gas may be heated by dissipation of turbulent energy. For the fractional total-NH₃ (para+ortho) abundance obtained by a comparison with Herschel infrared continuum data representing dust emission, we find values from 0.1 ×10⁻⁸ to 2.1 ×10⁻⁷ with an average of 6.9 (±4.5) × 10⁻⁸. Serpens South also shows a fractional total-NH₃ (para+ortho) abundance ranging from 0.2 ×10⁻⁸ to 2.1 ×10⁻⁷ with an average of 8.6 (±3.8) × 10⁻⁸. In W 40, values are lower, between 0.1 and 4.3 ×10⁻⁸ with an average of 1.6 (±1.4) × 10⁻⁸. Weak velocity gradients demonstrate that the rotational energy is a negligible fraction of the gravitational energy. In W 40, gas and dust temperatures are not strongly dependent on the projected distance to the recently formed massive stars. Overall, the morphology of the mapped region is ring-like, with strong emission at lower and weak emission at higher Galactic longitudes. However, the presence of a physical connection between the two parts remains questionable.