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 Δ n 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 H 2 CS, HCOOH, C 2 H 5 OH, H 2 13 CO, H 2 CCO, CH 3 CHO, CH 2 OCH 2 , HCN υ 2 = 1, and CH 3 OCHO υ t = 1. In particular, the vibrationally excited states of ethyl cyanide (C 2 H 5 CN υ 13/ υ 21) are for the first time firmly detected in the Q band. NH 3 (15,15) and (16,16) are identified, and they are so far the highest transitions of the NH 3 inversion lines detected toward Orion KL. All of the identified lines can be reproduced by a radiative transfer model.