A Q-band line survey towards Orion KL using the Tianma radio telescope
Abstract
We have conducted a line survey towards Orion KL using the Q-band receiver of Tianma 65 m radio telescope (TMRT), covering 34.8--50 GHz with a velocity resolution between 0.79 km s-1 and 0.55 km s-1 respectively. The observations reach a sensitivity on the level of 1-8 mK, proving that the TMRT is sensitive for conducting deep line surveys. In total, 597 Gaussian features are extracted. Among them, 177 radio recombination lines (RRLs) are identified, including 126, 40 and 11 RRLs of hydrogen, helium and carbon, with a maximum n of 16, 7, and 3, respectively. The carbon RRLs are confirmed to originate from photodissociation regions with a V LSR9 km s-1. In addition, 371 molecular transitions of 53 molecular species are identified. Twenty-one molecular species of this survey were not firmly detected in the Q band by Rizzo et al. (2017), including species such as H2CS, HCOOH, C2H5OH, H213CO, H2CCO, CH3CHO, CH2OCH2, HCN v2=1, and CH3OCHO vt=1. In particular, the vibrationally excited states of ethyl cyanide (C2H5CN v13/v21) are for the first time firmly detected in the Q band. NH3 (15,15) and (16,16) are identified, and they are so far the highest transitions of the NH3 inversion lines detected towards Orion KL. All the identified lines can be reproduced by a radiative transfer model.