A Q-band Line Survey toward Orion KL Using the Tianma Radio Telescope

Abstract

We have conducted a line survey toward Orion KL using the Q-band receiver of the Tianma 65 m radio telescope (TMRT), covering 34.8–50 GHz with a velocity resolution between 0.79 and 0.55 km s−1, respectively. The observations reach a sensitivity of 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 Δn of 16, 7, and 3, respectively. The carbon RRLs are confirmed to originate from photodissociation regions with a V LSR ∼ 9 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., including species such as H2CS, HCOOH, C2H5OH, CO, H2CCO, CH3CHO, CH2OCH2, HCN υ 2 = 1, and CH3OCHO υ t = 1. In particular, the vibrationally excited states of ethyl cyanide (C2H5CN υ13/υ21) 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 toward Orion KL. All of the identified lines can be reproduced by a radiative transfer model.