A map of OMC-1 in CO 9-8

The distribution of 12C16O 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 velocity-resolved 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 linewidthof 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^(3.5) cm^(-3) near theta^(1) C Ori and at the Orion Bar, and from 70 K gas at around 10^(4) cm^(-3) 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.