Detection of Extended Hot Water in the Outflow from NGC 2071

We report the results of spectroscopic mapping observations carried out toward an ~1′ × 1′ region within the northern lobe of the outflow from NGC 2071 using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations covered the 5.2-37 μm spectral region and have led to the detection of a number of ionic, atomic, and molecular lines, including fine-structure emission of Si+, Fe+, S++, S, the S(0)-S(7) pure rotational lines of H2, the R(3) and R(4) transitions of HD, and at least eleven transitions of H2O. In addition, the 6.2, 7.4, 7.6, 7.9, 8.6, and 11.3 μm PAH emission bands were also observed and several transitions of OH were tentatively detected. Most of the detected line transitions were strong enough to map, including, for the first time, three transitions of hot H2O. We find that (1) the water emission is extended; (2) the extended emission is aligned with the outflow; and (3) the spatial distribution of the water emission generally follows that observed for H2. Based on the measured line intensities, we derive an HD abundance relative to H2 of (1.1–1.8) × 10−5 and an H2O number density of 12-29 cm−3. The H2 density in the water-emitting region is not well constrained by our observations, but is likely between 3 × 104 and 106 cm−3, yielding an H2O abundance relative to H2 of between 2 × 10−5 and 6 × 10−4. Finally, we note a possible departure from the H2O ortho-to-para ratio of 3 : 1 expected for water formed in hot postshocked gas, suggesting that a significant fraction of the water vapor we detect may arise from H2O sputtered from cold dust grains.