The distribution of water in the high-mass star-forming region NGC 6334 I

Abstract

<i>Aims. <i/>We present observations of twelve rotational transitions of H<sub>2<sub/><sup>16<sup/>O, H<sub>2<sub/><sup>18<sup/>O, and H<sub>2<sub/><sup>17<sup/>O toward the massive star-forming region NGC 6334 I, carried out with <i>Herschel<i/>/HIFI as part of the guaranteed time key program Chemical <i>HErschel<i/> Surveys of Star forming regions (CHESS). We analyze these observations to obtain insights into physical processes in this region.<i>Methods. <i/>We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components. <i>Results. <i/>The hot core, identified by the emission in highly excited lines, shows a high excitation temperature of ~200 K, whereas water in the foreground component is predominantly in the ortho- and para- ground states. The abundance of water varies between 4 × 10<sup>-5<sup/> (outflow) and 10<sup>-8<sup/> (cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H<sub>2<sub/><sup>18<sup/>O/H<sub>2<sub/><sup>17<sup/>O abundance ratio is 3.2, which is consistent with the <sup>18<sup/>O/<sup>17<sup/>O ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low (1.6<i>±<i/>1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5<i>±<i/>0.8).