A Map of Omc-1 in Co J = 9 → 8

The distribution of CO J = 9 → 8 (1.037 THz) emission has been mapped in OMC-1 at 35 points with 84 resolution. This is the first map of this source in this transition and only the second velocityresolved ground-based observation of a line in the terahertz frequency band. There is emission present at all points in the map, a region roughly 4 by 6 in size, with peak antenna temperature dropping only near the edges. Away from the Orion KL outflow, the velocity structure suggests that most of the emission comes from the OMC-1 photon-dominated region, with a typical linewidth of 3-6 km s. Large velocity gradient modeling of the emission in J = 9 → 8 and six lower transitions suggests that the lines originate in regions with temperatures around 120 K and densities of at least 10 cm near θC Ori and at the Orion Bar, and from 70 K gas at around 10 cm southeast and west of the bar. These observations are among the first made with the 0.8 m Smithsonian Astrophysical Observatory Receiver Lab Telescope, a new instrument designed to observe at frequencies above 1 THz from an extremely high and dry site in northern Chile. Subject headings: ISM: clouds – ISM: individual: OMC-1 – ISM: individual: Orion Kleinmann-Low – ISM: individual: Orion Bar – submillimeter – telescopes