We present Herschel/HIFI observations of 30 transitions of water isotopologues toward the high-mass star forming region NGC 6334 I. The line profiles of H_2^{16}O, H_2^{17}O, H_2^{18}O, and HDO show a complex pattern of emission and absorption compon
ents associated with the embedded hot cores, a lower-density envelope, two outflow components, and several foreground clouds, some associated with the NGC 6334 complex, others seen in projection against the strong continuum background of the source. Our analysis reveals an H2O ortho/para ratio of 3 +/- 0.5 in the foreground clouds, as well as the outflow. The water abundance varies from ~10^{-8} in the foreground clouds and the outer envelope to ~10^{-6} in the hot core. The hot core abundance is two orders of magnitude below the chemical model predictions for dense, warm gas, but within the range of values found in other Herschel/HIFI studies of hot cores and hot corinos. This may be related to the relatively low gas and dust temperature (~100 K), or time dependent effects, resulting in a significant fraction of water molecules still locked up in dust grain mantles. The HDO/H_2O ratio in NGC 6334 I, ~2 10^{-4}, is also relatively low, but within the range found in other high-mass star forming regions.
We present Herschel/HIFI observations of nine transitions of hho and hheo towards six high-mass star-forming regions, obtained as part of the PRISMAS Key Program. Water vapor in translucent clouds is detected in absorption along every sightline. We d
erive the column density of hho or hheo for the lower energy level of each transition observed. The total water column density is about a few $10^{13} rm{cm^{-2}}$. We find that the abundance of water relative to hydrogen nuclei is $1times10^{-8}$ in agreement with models for oxygen chemistry with high cosmic ray ionization rates. Relative to hh, the abundance of water is remarkably constant at $5times10^{-8}$. The abundance of water in excited levels is at most 15%, implying that the excitation temperature $T_{ex}$ in the ground state transitions is below 10 K. The column densities derived from the two ortho ground state transitions indicates that $T_{ex}simeq5$ K and that the density $n($hh$)$ in the clouds is $le10^4 rm{cm^{-3}}$. For most clouds we derive a water ortho-to-para ratio consistent with the value of 3 expected in thermodynamic equilibrium in the high temperature limit. Two clouds with large column densities exhibit a ratio significantly below 3. This may argue that the history of water molecules includes a cold phase, either when the molecules were formed on cold grains, or when they later become at least partially thermalized with the cold gas ($sim25$ K) in the shielded, low temperature regions of the clouds; evidently, they have not yet fully thermalized with the warmer ($sim50$ K) translucent portions of the clouds.
We report a detection of the excited 220-211 rotational transition of para-H2O in APM 08279+5255 using the IRAM Plateau de Bure interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From LVG modeling, we c
onclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the HF J = 1 - 0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic ISM.
We present observations of twelve rotational transitions of H2O-16, H2O-18, and H2O-17 toward the massive star-forming region NGC 6334 I, carried out with Herschel/HIFI as part of the guaranteed time key program Chemical HErschel Surveys of Star form
ing regions (CHESS). We analyze these observations to obtain insights into physical processes in this region. We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components. 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^-5 (outflow) and 10^-8 (cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H2O-18/H2O-17 abundance ratio is 3.2, which is consistent with the O-18/O-17 ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low 1.6(1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5(0.8)).
We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H$_2^{16}$O and H$_2^{18}$O in absorption towards Sagittarius~B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sig
ht towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of $2.35 pm 0.35$, corresponding to a spin temperature of $sim$27~K, towards Sagittarius~B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.
We report the first detection of chloronium, H$_2$Cl$^+$, in the interstellar medium, using the HIFI instrument aboard the emph{Herschel} Space Observatory. The $2_{12}-1_{01}$ lines of ortho-H$_2^{35}$Cl$^+$ and ortho-H$_2^{37}$Cl$^+$ are detected i
n absorption towards NGC~6334I, and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ is detected in absorption towards NGC~6334I and Sgr~B2(S). The H$_2$Cl$^+$ column densities are compared to those of the chemically-related species HCl. The derived HCl/H$_2$Cl$^+$ column density ratios, $sim$1--10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H$_2$Cl$^+$ column densities, in excess of $10^{13}$~cm$^{-2}$, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models.
Using the Green Bank Telescope (GBT), we have obtained accurate measurements of the $^{14}$N/$^{15}$N isotopic ratio in ammonia in two nearby cold, dense molecular clouds, Barnard~1 and NGC 1333. The $^{14}$N/$^{15}$N ratio in Barnard~1, $334 pm 50$
(3$sigma$), is particularly well constrained and falls in between the local interstellar medium/proto-solar value of $sim 450$ and the terrestrial atmospheric value of 272. The NGC 1333 measurement is consistent with the Barnard~1 result, but has a larger uncertainty. We do not see evidence for the very high $^{15}$N enhancements seen in cometary CN. Sensitive observations of a larger, carefully selected sample of prestellar cores with varying temperatures and gas densities can significantly improve our understanding of the nitrogen fractionation in the local interstellar medium and its relation to the isotopic ratios measured in various solar system reservoirs.
