1996A&A...314..281G

We have detected the quasi-thermal 3₁₃-2₂₀ line of H₂¹⁸O with a 12" resolution in 13 of 26 galactic sources of massive star formation. No lines were detected toward 6 evolved stars. We also made searches for deuterated water, HDO, in the 4₂₂-4₂₃ and 3₁₂-2₂₁ transitions, detecting 9 sources of HDO emission. Using an LTE analysis, we infer that the average fractional abundance of gas phase water, [H₂O]/[H₂], toward the sources in our sample is ∼10^–5. The ratio [HDO]/[H₂O] is ∼3x10^–4. The inferred [HDO]/[H₂O] ratio should be much more reliable than the [H₂O]/[H₂] ratio since the column density of H₂ is rather uncertain. Our maps of H₂¹⁸O and HDO toward Orion IRc2 and Sgr B2 indicate that the emission from these sources is small compared to the size of the telescope beam. Toward Sgr B2, the emission from H₂¹⁸O peaks on Sgr B2(N); if there is any emission toward Sgr B2(M), it is 25% the intensity of the emission from Sgr B2(N). The inferred abundances, compact sizes and distributions of the emission regions lead us to believe that evaporation of grain mantles in the hot cores of massive star forming regions must play an important role in the formation of interstellar gas phase water in these regions. Implications concerning the oxygen budget of the interstellar medium and the cooling of hot molecular cloud cores are also discussed.