Submillimeter Wave Astronomy Satellite Observations of Extended Water Emission in Orion

We have used the Submillimeter Wave Astronomy Satellite to map the ground-state 110 → 101 transition of ortho-H2O at 557 GHz in the Orion molecular cloud. H2O emission was detected in Orion over an angular extent of about 20, or nearly 3 pc. The water emission is relatively weak, with line widths (3–6 km s−1) and VLSR velocities (9–11 km s−1) consistent with an origin in the cold gas of the molecular ridge. We find that the orthoH2O abundance relative to H2 in the extended gas in Orion varies between 1 and 8×10−8, with an average of 3×10−8. The absence of detectable narrow-line ortho-H18 2 O emission is used to set a 3σ upper limit on the relative ortho-H2O abundance of 7×10−8. Subject headings: ISM: abundances — ISM: clouds — ISM: individual (Orion) — ISM: molecules — radio lines: ISM