Star-forming regions of the Aquila rift cloud complex

I. NH₃ tracers of dense molecular cores^⋆

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
² Ioffe Physical-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia
e-mail: lev@astro.ioffe.rssi.ru
³ St. Petersburg Electrotechnical University “LETI”, Prof. Popov Str. 5, 197376 St. Petersburg, Russia
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Astronomy Department, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia
⁶ Purple Mountain Observatory, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, PR China

Received: 10 September 2012
Accepted: 7 March 2013

Abstract

Aims. The physics of star formation is an important part of Galactic evolution. Most stars are formed in high-density environments (n > 10⁴ cm^-3) and emit lines of diverse molecular transitions. In the present part of our survey we search for ammonia emitters in the Aquila rift complex, which trace the densest regions of molecular clouds.

Methods. From a CO survey carried out with the Delingha 14-m telescope we selected ~150 targets for observations in other molecular lines. Here we describe the mapping observations in the NH₃(1, 1) and (2, 2) inversion lines of the first 49 sources performed with the Effelsberg 100-m telescope.

Results. The NH₃(1, 1) emission lines are detected in 12 and the (2, 2) in 7 sources. Among the newly discovered NH₃ sources, our sample includes the following well-known clouds: the starless core L694-2, the Serpens cloud cluster B, the Serpens dark cloudL572, the filamentary dark cloud L673, the isolated protostellar source B335, and the complex star-forming region Serpens South. Angular sizes between 40′′ and 80′′ (~0.04–0.08 pc) are observed for compact starless cores but can be as large as 9′ (~0.5 pc) for filamentary dark clouds. The measured kinetic temperatures of the clouds lie between 9 K and 18 K. From NH₃ excitation temperatures of 3–8 K we determine H₂ densities with typical values of ~ (0.4−4) × 10⁴ cm^-3. The masses of the mapped cores range between ~0.05 and ~ 0.5  M_⊙. The relative ammonia abundance X = [NH₃]/[H₂] varies from 1 × 10^-7 to 5 × 10^-7 with the mean ⟨ X ⟩  = (2.7 ± 0.6) × 10^-7 (estimated from spatially resolved cores assuming a filling factor of η = 1). In two clouds, we observe kinematically split NH₃ profiles separated by ~1 km s^-1. The splitting is most likely due to bipolar molecular outflows, for one of which we determine an acceleration of V ̇ ≲ 0.03 km s^-1 yr^-1. A starless core with significant rotational energy is found to have a higher kinetic temperature than the other ones, which is probably caused by magnetic energy dissipation.