Ground-based terahertz CO spectroscopy towards Orion

Abstract

Using a superconductive hot-electron bolometer heterodyne receiver on the 10-m Heinrich Hertz Telescope on Mount Graham, Arizona, we have obtained velocity-resolved 1.037 THz CO (J = 9 → 8) spectra toward several positions along the Orion Molecular Cloud (OMC-1) ridge. We confirm the general results of prior observations of high-J CO lines that show that the high temperature, T_(kin) ≥ 130 K, high density molecular gas, N ≥ 10^6 cm^(-3), is quite extended, found along a ~ 4' region centered on BN/KL. However, our observations have significantly improved angular resolution, and with a beam size of θ_(FWHP) we are able to spatially and kinematically discriminate the emission originating in the extended quiescent ridge from the very strong and broadened emission originating in the compact molecular outflow. The ridge emission very close to the BN/KL region appears to originate from two distinct clouds along the line of sight with v_(LSR) ≈ +6(1)kms^(-1) and ≈ +10(1)km s^(-1). The former component dominates the emission to the south of BN/KL and the latter to the north, with a turnover point coincident with or near BN/KL. Our evidence precludes a simple rotation of the inner ridge and lends support to a model in which there are multiple molecular clouds along the line of sight towards the Orion ridge.