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L’incitation indue est un risque largement connu en recherche biomédicale, il est particulièrement prégnant en contexte de pauvreté et de difficulté d’accès aux soins. Néanmoins, il serait inapproprié de dénoncer l’incitation indue de manière paternaliste et donneuse de leçons, en déniant aux personnes dans les communautés pauvres l’aptitude de juger de ce qui est bon pour elles et pour leurs enfants. Dans cette optique, l’incitation devrait être reconnue comme un phénomène intrinsèque à la recherche et non fondamentalement éliminatoire au déroulement d’une étude donnée. Il est important que les contours et les caractéristiques de ce phénomène soient le plus clairement définis, pour que les comités d’éthique de la recherche puissent l’identifier et prendre des mesures pour réduire ses impacts négatifs.

Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH+, is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH+(J = 1–0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH+emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH+absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.

Aims. Supersonic turbulence is a large reservoir of suprathermal energy in the interstellar medium. Its dissipation, because it is intermittent in space and time, can deeply modify the chemistry of the gas. This is clearly seen in the framework of shock chemistry. Intense turbulent dissipation also occurs in regions of large velocity shears, sharing with shocks the property of intermittency. Whether these bursts of dissipation, short-lived and localized, have a measurable impact on molecular abundances in the diffuse medium, and how the chemical enrichment they drive compares to observations, are the questions we address here.

Nutrigenomics covers disparate fields of nutrition science and has been defined in many different ways. In fact, this emerging field of science has multiple facets, many of which do not generate the same ethical issues. In particular, different ethical issues emerge concerning the extent to which nutrigenomics may actually improve global health, i.e., in terms of worldwide improvement of health, reduction of disparities, and protection against global threats that disregard national borders. Nutrigenomics raises many hopes and expectations on that score. However, it remains unclear and controversial whether nutrigenomics studies and their actual or potential applications will actually benefit developing countries and their populations. Different forces may drive the choice of research priorities and shape the claims that are made when communicating the goals or the results of nutrigenomics studies and applications. This article proposes to assess expectations and claims in nutrigenomics, with respect to their respective potential impact on global health and the ethical issues they raise. Nutrigenomics is and should be more than premature claims and much debated promises about personalized nutritional interventions on individuals. Beyond questionable commercial claims, nutrigenomics is also knowledge about and recognition of the considerable impacts of underfeeding and malnutrition on the genome (and epigenome) integrity and stability. As such, nutrigenomics research is a valuable opportunity to revive and give strength to the debate about the unacceptable consequences of hunger and malnutrition worldwide, and to support a newly and potentially significant convergence in research priorities that could benefit both developed and developing countries.

Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer(FUSE) has made over 4900 observations of some 2500 individual targets. The data are reduced by the principal investigator team at the Johns Hopkins University and archived at the Multimission Archive at STScI (MAST). The data reduction software package, called CalFUSE, has evolved considerably over the lifetime of the mission. The entire FUSEdata set has recently been reprocessed with CalFUSE version 3.2, the latest version of this software. This paper describes CalFUSE version 3.2, the instrument calibrations on which it is based, and the format of the resulting calibrated data files.

Les résultats de l’essai NLST ont ouvert le débat sur l’opportunité d’un programme de dépistage du cancer bronchopulmonaire (CBP) chez les personnes exposées à des cancérigènes respiratoires. L’objectif de ce travail est l’analyse coût–efficacité d’un programme de dépistage du CBP dans une cohorte de sujets exposés à l’amiante.

Using the IRAM 30 m telescope we observed molecular absorption lines from CCH and c-C3H2produced by diffuse and translucent clouds along the lines of sight towards massive star forming regions. The same sources are surveyed with Herschel/HIFI as part of the PRISMAS guaranteed time program, for molecular absorption lines due to hydrides and carbon clusters. The background sources are massive star-forming regions (G34.3 + 0.1, G10.62−0.39, W51, W49N) and SgrA∗ . The line profiles of the CCH  and c-C3H2are strikingly similar for all lines of sight, showing that the ratio of the opacities of the probed transitions, (JKa,Kc= 21,2−10,1) for c-C3H2and (J= 1−0,F= 5/2−3/2) for CCH, is nearly constant along all lines of sight, at τCCH~ 1.8 × τc - C3H2. As a consequence, the ratio of the column densities of CCH and c-C3H2is nearly constant and similar to the value derived earlier for diffuse clouds detected along lines of sight towards extragalactic continuum sources, N(CCH) = (28 ± 1.4)N(c - C3H2) (Lucas & Liszt 2000, A&A, 358, 1069). PDR models are able to reproduce the observed CCH  column densities for the range of physical conditions appropriate for the absorbing matter (n= 100−3000 cm-3; AV= 1−5 mag) but can neither fit the observed c-C3H2column densities nor the tight correlation between CCH  and c-C3H2.

We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N= 1–0 transition of OH+and the 1115 GHz 111–000transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s-1with respect to the local standard of rest. The inferred OH+/H2O+abundance ratio ranges from ~3 to ~15, implying that the observed OH+arises in clouds of small molecular fraction, in the 2–8% range. This conclusion is confirmed by the distribution of OH+and H2O+in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few ×10-8suggests a cosmic ray ionization rate for atomic hydrogen of 0.6–2.4×10-16s-1, in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H3+and other species.

We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H216O and H218O in absorption towards Sagittarius B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight 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 ±0.35, corresponding to a spin temperature of ~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 present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy ν2bending mode at frequencies between 1654–1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel's HIFI instrument. We detect C3in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C3absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (Trot) of ~50-70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived Trot, we get column densities N(C3) ~ 7–9 × 1014cm-2and abundance x(C3) ~ 10-8with respect to H2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C3) = 10-8, Tkin= 30–50 K, N(C3) = 1.5 × 1015cm-2fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis.

The HIFI instrument on board the HerschelSpace Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N= 1 $\leftarrow$0, J= 2 $\leftarrow$1 and ortho-NH211,1$\gets$00,0. We also observed ortho-NH310$\gets$00, and 20$\gets$10, para-NH321$\gets$11, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km s-1are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6× 10-9, 3× 10-9, and 3× 10-9for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry.

We report the detection of the ground state N,J= 1,3/2 $\rightarrow$1,1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emissionlines, clouds in the diffuse interstellar medium are detected in absorptionagainst the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO+in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO+deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with [CCH]/[ H2] ~ 3.2±1.1×10-8. The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities nH= n(H) + 2n(H2) ranging between 100 and 1000 cm-3.

We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J= 1–0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure– as opposed to obtain a lower limit on – the column density of HF for the first time. As in previous observations of HF toward the source G10.6–0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)–N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H2column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~24 km s-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel.

We report the detection of the ground-state rotational transition of the methylidyne cation CH+and its isotopologue 13CH+toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschelsatellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12CH+] /[ 13CH+]  >35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12CH+average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH> 2.6×10-8, is higher than that observed in the solar neighborhood and confirms the high abundances of CH+in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/N(HCO+) ratios, from 1 to ~50, is comparable to that observed.

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 sight 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 ±0.35, corresponding to a spin temperature of ~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 detection of the ground state N,J= 1,3/2 $\rightarrow$1,1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emissionlines, clouds in the diffuse interstellar medium are detected in absorptionagainst the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO+in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO+deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with [CCH]/[ H2] ~ 3.2±1.1×10-8. The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities nH= n(H) + 2n(H2) ranging between 100 and 1000 cm-3.

We report the detection of the ground-state rotational transition of the methylidyne cation CH+and its isotopologue 13CH+toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschelsatellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12CH+] /[ 13CH+]  >35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12CH+average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH> 2.6×10-8, is higher than that observed in the solar neighborhood and confirms the high abundances of CH+in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/N(HCO+) ratios, from 1 to ~50, is comparable to that observed.

The HIFI instrument on board the HerschelSpace Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N= 1 $\leftarrow$0, J= 2 $\leftarrow$1 and ortho-NH211,1$\gets$00,0. We also observed ortho-NH310$\gets$00, and 20$\gets$10, para-NH321$\gets$11, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km s-1are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6× 10-9, 3× 10-9, and 3× 10-9for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry.

We present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy ν2bending mode at frequencies between 1654–1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel's HIFI instrument. We detect C3in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C3absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (Trot) of ~50-70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived Trot, we get column densities N(C3) ~ 7–9 × 1014cm-2and abundance x(C3) ~ 10-8with respect to H2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C3) = 10-8, Tkin= 30–50 K, N(C3) = 1.5 × 1015cm-2fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis.

We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J= 1–0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure– as opposed to obtain a lower limit on – the column density of HF for the first time. As in previous observations of HF toward the source G10.6–0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)–N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H2column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~24 km s-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel.

We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N= 1–0 transition of OH+and the 1115 GHz 111–000transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s-1with respect to the local standard of rest. The inferred OH+/H2O+abundance ratio ranges from ~3 to ~15, implying that the observed OH+arises in clouds of small molecular fraction, in the 2–8% range. This conclusion is confirmed by the distribution of OH+and H2O+in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few × 10-8suggests a cosmic ray ionization rate for atomic hydrogen of 0.6–2.4×10-16s-1, in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H3+and other species.

Aims. The comparative study of several molecular species at the origin of the gas phase chemistry in the diffuse interstellar medium (ISM) is a key input in unraveling the coupled chemical and dynamical evolution of the ISM.Methods. The lowest rotational lines of HCO+, HCN, HNC, and CN were observed at the IRAM-30m telescope in absorption against the λ3 mm and λ1.3 mm continuum emission of massive star-forming regions in the Galactic plane. The absorption lines probe the gas over kiloparsecs along these lines of sight. The excitation temperatures of HCO+are inferred from the comparison of the absorptions in the two lowest transitions. The spectra of all molecular species on the same line of sight are decomposed into Gaussian velocity components. Most appear in all the spectra of a given line of sight. For each component, we derived the central opacity, the velocity dispersion, and computed the molecular column density. We compared our results to the predictions of UV-dominated chemical models of photodissociation regions (PDR models) and to those of non-equilibrium models in which the chemistry is driven by the dissipation of turbulent energy (TDR models).Results. The molecular column densities of all the velocity components span up to two orders of magnitude. Those of CN, HCN, and HNC are linearly correlated with each other with mean ratios N(HCN)/N(HNC) = 4.8 ±1.3 and N(CN)/N(HNC) = 34 ±12, and more loosely correlated with those of HCO+, N(HNC)/N(HCO+) = 0.5 ±0.3, N(HCN)/N(HCO+) = 1.9 ±0.9, and N(CN)/N(HCO+) = 18 ±9. These ratios are similar to those inferred from observations of high Galactic latitude lines of sight, suggesting that the gas sampled by absorption lines in the Galactic plane has the same chemical properties as that in the Solar neighbourhood. The FWHMof the Gaussian velocity components span the range 0.3 to 3 km s-1and those of the HCO+lines are found to be 30% broader than those of CN-bearing molecules.
The PDR models fail to reproduce simultaneously the observed abundances of the CN-bearing species and HCO+, even for high-density material (100cm-3< nH< 104cm-3). The TDR models, in turn, are able to reproduce the observed abundances and abundance ratios of all the analysed molecules for the moderate gas densities (30 cm-3< nH< 200 cm-3) and the turbulent energy observed in the diffuse interstellar medium.Conclusions. Intermittent turbulent dissipation appears to be a promising driver of the gas phase chemistry of the diffuse and translucent gas throughout the Galaxy. The details of the dissipation mechanisms still need to be investigated.

Aims. The comparative study of several molecular species at the origin of the gas phase chemistry in the diffuse interstellar medium (ISM) is a key input in unraveling the coupled chemical and dynamical evolution of the ISM.

We report the first detection of the ground-state rotational transition of the methylidyne cation CH+towards the massive star-forming region DR 21 with the HIFI instrument onboard the Herschelsatellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR 21 molecular ridge and foreground gas. These observations allow us to determine a 12CH+J= 1–0 line frequency of ν= 835 137 ±3MHz, in good agreement with a recent experimental determination. We estimate the CH+column density to be a few 1013cm-2in the gas seen in emission, and >1014cm-2in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+] /[H] > 1.2 × 10-8. We show that the CH+column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.

We report the detection of absorption lines by the reactive ions OH+, H2O+and H3O+along the line of sight to the submillimeter continuum source G10.6–0.4 (W31C). We used the HerschelHIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+at 971 GHz, H2O+at 1115 and 607 GHz, and H3O+at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6–0.4 as well as in the molecular gas directly associated with that source. The OH+spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+lines remains lower than 1 in the same velocity range, and the H3O+line shows only weak absorption. For LSR velocities between 7 and 50 km s-1we estimate total column densities of N(OH+) ≥2.5 × 1014cm-2, N(H2O+) ~6 × 1013cm-2and N(H3O+) ~4.0 × 1013cm-2. These detections confirm the role of O+and OH+in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+by the H2O+column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.

We report the detection of strong absorption by interstellar hydrogen fluoride along the sight-line to the submillimeter continuum source G10.6–0.4 (W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 1232.4763 GHz J= 1–0 HF transition in the upper sideband of the Band 5a receiver. The resultant spectrum shows weak HF emission from G10.6–0.4 at LSR velocities in the range –10 to –3 km s-1, accompanied by strong absorption by foreground material at LSR velocities in the range 15 to 50 km s-1. The spectrum is similar to that of the 1113.3430 GHz 111–000transition of para-water, although at some frequencies the HF (hydrogen fluoride) optical depth clearly exceeds that of para-H2O. The optically-thick HF absorption that we have observed places a conservative lower limit of 1.6×1014cm-2on the HF column density along the sight-line to G10.6–0.4. Our lower limit on the HF abundance, 6×10-9relative to hydrogen nuclei, implies that hydrogen fluoride accounts for between ~30% and 100% of the fluorine nuclei in the gas phase along this sight-line. This observation corroborates theoretical predictions that – because the unique thermochemistry of fluorine permits the exothermic reaction of F atoms with molecular hydrogen – HF will be the dominant reservoir of interstellar fluorine under a wide range of conditions.

We report the detection of absorption lines by the reactive ions OH+, H2O+and H3O+along the line of sight to the submillimeter continuum source G10.6–0.4 (W31C). We used the HerschelHIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+at 971 GHz, H2O+at 1115 and 607 GHz, and H3O+at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6–0.4 as well as in the molecular gas directly associated with that source. The OH+spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+lines remains lower than 1 in the same velocity range, and the H3O+line shows only weak absorption. For LSR velocities between 7 and 50 km s-1we estimate total column densities of N(OH+) ≥2.5 × 1014cm-2, N(H2O+) ~6 × 1013cm-2and N(H3O+) ~4.0 × 1013cm-2. These detections confirm the role of O+and OH+in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+by the H2O+column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.

We report the detection of strong absorption by interstellar hydrogen fluoride along the sight-line to the submillimeter continuum source G10.6–0.4 (W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 1232.4763 GHz J= 1–0 HF transition in the upper sideband of the Band 5a receiver. The resultant spectrum shows weak HF emission from G10.6–0.4 at LSR velocities in the range –10 to –3 km s-1, accompanied by strong absorption by foreground material at LSR velocities in the range 15 to 50 km s-1. The spectrum is similar to that of the 1113.3430 GHz 111–000transition of para-water, although at some frequencies the HF (hydrogen fluoride) optical depth clearly exceeds that of para-H2O. The optically-thick HF absorption that we have observed places a conservative lower limit of 1.6×1014cm-2on the HF column density along the sight-line to G10.6–0.4. Our lower limit on the HF abundance, 6×10-9relative to hydrogen nuclei, implies that hydrogen fluoride accounts for between ~30% and 100% of the fluorine nuclei in the gas phase along this sight-line. This observation corroborates theoretical predictions that – because the unique thermochemistry of fluorine permits the exothermic reaction of F atoms with molecular hydrogen – HF will be the dominant reservoir of interstellar fluorine under a wide range of conditions.

We report the first detection of the ground-state rotational transition of the methylidyne cation CH+towards the massive star-forming region DR 21 with the HIFI instrument onboard the Herschelsatellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR 21 molecular ridge and foreground gas. These observations allow us to determine a 12CH+J= 1–0 line frequency of ν= 835 137 ±3MHz, in good agreement with a recent experimental determination. We estimate the CH+column density to be a few 1013cm-2in the gas seen in emission, and >1014cm-2in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+] /[H] > 1.2 × 10-8. We show that the CH+column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.