Search

Context. Only recently, OD, the deuterated isotopolog of hydroxyl, OH, has become accessible in the interstellar medium; spectral lines from both species have been observed in the supra-Terahertz and far infrared regime. Studying variations of the OD/OH abundance amongst different types of sources can deliver key information on the formation of water, H2O. Aims. With observations of rotational lines of OD and OH towards 13 Galactic high-mass star forming regions, we aim to constrain the OD abundance and infer the deuterium fractionation of OH in their molecular envelopes. For the best studied source in our sample, G34.26+0.15, we were able to perform detailed radiative transfer modelling to investigate the OD abundance profile in its inner envelope. Methods. We used the Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe the (2)pi(3/2) J = 5/2-3/2 ground-state transition of OD at 1.3 THz (215 mu m) and the rotationally excited OH line at 1.84 THz (163 mu m). We also used published high-spectral-resolution SOFIA data of the OH ground-state transition at 2.51 THz (119.3 mu m). Results. Absorption from the (2)pi(3/2) OD J = 5/2-3/2 ground-state transition is prevalent in the dense clumps surrounding active sites of high-mass star formation. Our modelling suggests that part of the absorption arises from the denser inner parts, while the bulk of it as seen with SOFIA originates in the outer, cold layers of the envelope for which our constraints on the molecular abundance suggest a strong enhancement in deuterium fractionation. We find a weak negative correlation between the OD abundance and the bolometric luminosity to mass ratio, an evolutionary indicator, suggesting a slow decrease of OD abundance with time. A comparison with HDO shows a similarly high deuterium fractionation for the two species in the cold envelopes, which is of the order of 0.48% for the best studied source, G34.26+0.15. Conclusions. Our results are consistent with chemical models tha

Aims. Revealing the 3D dynamics of H-II region bubbles and their associated molecular clouds and H-I envelopes is important for developing an understanding of the longstanding problem as to how stellar feedback affects the density structure and kinematics of the different phases of the interstellar medium. Methods. We employed observations of the H-II region RCW 120 in the [C-II] 158 mu m line, observed within the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program FEEDBACK, and in the (CO)-C-12 and (CO)-C-13 (3 -> 2) lines, obtained with the Atacama Pathfinder Experiment (APEX) to derive the physical properties of the gas in the photodissociation region (PDR) and in the molecular cloud. We used high angular resolution H-I data from the Southern Galactic Plane Survey to quantify the physical properties of the cold atomic gas through H-I self-absorption. The high spectral resolution of the heterodyne observations turns out to be essential in order to analyze the physical conditions, geometry, and overall structure of the sources. Two types of radiative transfer models were used to fit the observed [C-II] and CO spectra. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. To fully exploit the spectral-spatial information in the CO spectra, a Gaussian mixture model was introduced that allows for grouping spectra into clusters with similar properties. Results. The CO emission arises mostly from a limb-brightened, warm molecular ring, or more specifically a torus when extrapolated in 3D. There is a deficit of CO emission along the line-of-sight toward the center of the H-II region which indicates that the H-II region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of i

Context. The [C II] 158 mu m fine-structure line is the dominant cooling line of moderate-density photodissociation regions (PDRs) illuminated by moderately bright far-ultraviolet (FUV) radiation fields. This makes this line a prime diagnostic for extended regions illuminated by massive stars. Aims. We aim to understand the origin of [C II] emission and its relation to other tracers of gas and dust in PDRs. One focus is a study of the heating efficiency of interstellar gas as traced by the [C II] line to test models of the photoelectric heating of neutral gas by polycyclic aromatic hydrocarbon (PAH) molecules and very small grains. Methods. We make use of a one-square-degree map of velocity-resolved [C II] line emission toward the Orion Nebula complex, and split this out into the individual spatial components, the expanding Veil Shell, the surface of OMC4, and the PDRs associated with the compact H II region of M43 and the reflection nebula NGC 1977. We employed Herschel far-infrared photometric images to determine dust properties. Moreover, we compared with Spitzer mid-infrared photometry to trace hot dust and large molecules, and velocity-resolved IRAM 30m CO(2-1) observations of the molecular gas. Results. The [C II] intensity is tightly correlated with PAH emission in the IRAC 8 mu m band and far-infrared emission from warm dust, with small variations between the four studied subregions (Veil Shell, OMC4, M43, and NGC 1977). The correlation between [C II] and CO(2-1) is very different in the four subregions and is very sensitive to the detailed geometry of the respective regions. Constant-density PDR models are able to reproduce the observed [C II], CO(2-1), and integrated far-infrared (FIR) intensities. The physical conditions in the Veil Shell of the Orion Nebula, M43, and NGC 1977 reveal a constant ratio of thermal pressure p(th) over incident FUV radiation field measured by G(0). We observe strong variations in the photoelectric heating efficiency in the Vei

Context. The [CII] 158 mu m far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium. Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation. Aims. We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory. Methods. A 1.15 square degree velocity-resolved map of the Orion molecular cloud centred on the bar region was observed using the German REceiver for Astronomy at Terahertz Frequencies (upGREAT) heterodyne receiver flying on board the Stratospheric Observatory for Infrared Astronomy. The data were acquired using the 14 pixels of the German REceiver for Astronomy at Terahertz Frequencies that were observed in an on-the-fly mapping mode. 2.4 million spectra were taken in total. These spectra were gridded into a three-dimensional cube with a spatial resolution of 14.1 arcseconds and a spectral resolution of 0.3 km s(-1). Results. A square-degree [CII] map with a spectral resolution of 0.3 km s(-1) is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map tak

Context. The [CII] 158 mu m fine-structure line is one of the dominant coolants of the neutral interstellar medium. It is hence one of the brightest far-infrared (FIR) emission lines and can be observed not only in star-forming regions throughout the Galaxy, but also in the diffuse interstellar medium and in distant galaxies. [CII] line emission has been suggested to be a powerful tracer of star formation.Aims. We aim to understand the origin of [CII] emission and its relation to other tracers of interstellar gas and dust. This includes a study of the heating efficiency of interstellar gas as traced by the [CII] line to test models of gas heating.Methods. We made use of a one-square-degree map of velocity-resolved [CII] line emission toward the Orion Nebula complex, including M 43 and NGC 1977. We employed Herschel FIR photometric images to determine dust properties. Moreover, we compared with H alpha emission from the ionized gas, Spitzer mid-infrared photometry to trace hot dust and large polycyclic aromatic hydrocarbons (PAHs), and velocity-resolved IRAM 30m CO(2-1) observations of the molecular gas.Results. The [CII] intensity is tightly correlated with PAH emission in the IRAC 8 mu m band and FIR emission from warm dust. However, the [CII] intensity depends less than linearly on the 8 mu m and FIR intensity, while 8 mu m and FIR intensities are approximately linearly correlated. The correlation between [CII] and CO(2-1) does not show a clear trend and is affected by the detailed geometry of the region. We find particularly low [CII]-over-FIR intensity ratios toward large columns of (warm and cold) dust, which suggest the interpretation of the [CII] deficit in terms of a FIR excess.Conclusions. In terms of the [CII] deficit, we find clear evidence in our data for the importance of [OI] 63 mu m emission in the photodissociation regions (PDRs) associated with the Huygens region. A smaller contribution is made by a decreased heating efficiency in regions of high UV

Context. The Arches Cluster - Arched Filaments (AF) system is our Galaxy's prime example of the complexity involved in the interaction between the strong radiation field of numerous OB stars and their surrounding ISM in extremely harsh environments such as the Galactic center (GC) of the Milky Way. It offers a unique opportunity to study the close relationship between photon-dominated regions (PDRs) and H II regions and their relative contributions to the observed [CII] emission. Aims. We aim to investigate the I([CII]) versus I([NII]) integrated intensity behavior in the AF region in order to assess the [CII] emission contribution from the H II region, which is traced by [NII] line observations, and PDR components in the high-metallicity environment of the GC. Methods. We used [CII] 158 mu m and [NII] 205 mu m fine structure line observations of the AF in the literature to compare their observational integrated intensity distribution to semi-theoretical predictions for the contribution of H II regions and adjacent PDRs to the observed [CII] emission. We explored variations in the [C/N] elemental abundance ratio to explain the overall behavior of the observed relationship. Based on our models, the H II region and PDR contributions to the observed [CII] emission is calculated for a few positions within and near to the AF. Estimates for the [C/N] abundance ratio and [N/H] nitrogen elemental abundance in the AF can then be derived. Results. The behavior of the I([CII]) versus I([NII]) relationship in the AF can be explained by model results satisfying 0.84 < [C/N](AF) < 1.41, with model metallicities ranging from 1 Z(circle dot) to 2 Z(circle dot), hydrogen volume density log n(H) = 3.5, and ionization parameters log U from -1 to -2. A least-squares fit to the model data points yields log I([CII]) = 1.068 x log I([NII]) + 0.645 to predict the [CII] emission arising from the H II regions in the AF. The fraction of the total observed [CII] emission arising from within PD

Context. The [CII] 158 mu m far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium. Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation. Aims. We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory. Methods. A 1.15 square degree velocity-resolved map of the Orion molecular cloud centred on the bar region was observed using the German REceiver for Astronomy at Terahertz Frequencies (upGREAT) heterodyne receiver flying on board the Stratospheric Observatory for Infrared Astronomy. The data were acquired using the 14 pixels of the German REceiver for Astronomy at Terahertz Frequencies that were observed in an on-the-fly mapping mode. 2.4 million spectra were taken in total. These spectra were gridded into a three-dimensional cube with a spatial resolution of 14.1 arcseconds and a spectral resolution of 0.3 km s(-1). Results. A square-degree [CII] map with a spectral resolution of 0.3 km s(-1) is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map tak

Context. The [CII] 158 mu m fine-structure line is one of the dominant coolants of the neutral interstellar medium. It is hence one of the brightest far-infrared (FIR) emission lines and can be observed not only in star-forming regions throughout the Galaxy, but also in the diffuse interstellar medium and in distant galaxies. [CII] line emission has been suggested to be a powerful tracer of star formation.Aims. We aim to understand the origin of [CII] emission and its relation to other tracers of interstellar gas and dust. This includes a study of the heating efficiency of interstellar gas as traced by the [CII] line to test models of gas heating.Methods. We made use of a one-square-degree map of velocity-resolved [CII] line emission toward the Orion Nebula complex, including M 43 and NGC 1977. We employed Herschel FIR photometric images to determine dust properties. Moreover, we compared with H alpha emission from the ionized gas, Spitzer mid-infrared photometry to trace hot dust and large polycyclic aromatic hydrocarbons (PAHs), and velocity-resolved IRAM 30m CO(2-1) observations of the molecular gas.Results. The [CII] intensity is tightly correlated with PAH emission in the IRAC 8 mu m band and FIR emission from warm dust. However, the [CII] intensity depends less than linearly on the 8 mu m and FIR intensity, while 8 mu m and FIR intensities are approximately linearly correlated. The correlation between [CII] and CO(2-1) does not show a clear trend and is affected by the detailed geometry of the region. We find particularly low [CII]-over-FIR intensity ratios toward large columns of (warm and cold) dust, which suggest the interpretation of the [CII] deficit in terms of a FIR excess.Conclusions. In terms of the [CII] deficit, we find clear evidence in our data for the importance of [OI] 63 mu m emission in the photodissociation regions (PDRs) associated with the Huygens region. A smaller contribution is made by a decreased heating efficiency in regions of high UV

Context. The Arches Cluster - Arched Filaments (AF) system is our Galaxy's prime example of the complexity involved in the interaction between the strong radiation field of numerous OB stars and their surrounding ISM in extremely harsh environments such as the Galactic center (GC) of the Milky Way. It offers a unique opportunity to study the close relationship between photon-dominated regions (PDRs) and H II regions and their relative contributions to the observed [CII] emission. Aims. We aim to investigate the I([CII]) versus I([NII]) integrated intensity behavior in the AF region in order to assess the [CII] emission contribution from the H II region, which is traced by [NII] line observations, and PDR components in the high-metallicity environment of the GC. Methods. We used [CII] 158 mu m and [NII] 205 mu m fine structure line observations of the AF in the literature to compare their observational integrated intensity distribution to semi-theoretical predictions for the contribution of H II regions and adjacent PDRs to the observed [CII] emission. We explored variations in the [C/N] elemental abundance ratio to explain the overall behavior of the observed relationship. Based on our models, the H II region and PDR contributions to the observed [CII] emission is calculated for a few positions within and near to the AF. Estimates for the [C/N] abundance ratio and [N/H] nitrogen elemental abundance in the AF can then be derived. Results. The behavior of the I([CII]) versus I([NII]) relationship in the AF can be explained by model results satisfying 0.84 < [C/N](AF) < 1.41, with model metallicities ranging from 1 Z(circle dot) to 2 Z(circle dot), hydrogen volume density log n(H) = 3.5, and ionization parameters log U from -1 to -2. A least-squares fit to the model data points yields log I([CII]) = 1.068 x log I([NII]) + 0.645 to predict the [CII] emission arising from the H II regions in the AF. The fraction of the total observed [CII] emission arising from within PD

Context. Carbon molecules and their C-13-isotopologues can be used to determine the C-12/C-13 abundance ratios in stellar and interstellar objects. C-3 is a pure carbon chain molecule found in star-forming regions and in stellar shells of carbon-rich late-type stars. Latest laboratory data of C-13-isotopologues of C-3 allow a selective search for the mono-substituted species (CCC)-C-13 and (CCC)-C-13 based on accurate ro-vibrational frequencies. Aims. We aim to provide the first detection of the C-13-isotopologues (CCC)-C-13 and (CCC)-C-13 in space and to derive the C-12/C-13 ratio of interstellar gas in the massive star-forming region SgrB2(M) near the Galactic Center. Methods. We used the heterodyne receivers GREAT and upGREAT on board SOFIA to search for the ro-vibrational transitions Q(2) and Q(4) of (CCC)-C-13 and (CCC)-C-13 at 1.9 THz along the line of sight towards SgrB2(M). In addition, to determine the local excitation temperature, we analyzed data from nine ro-vibrational transitions of the main isotopologue CCC in the frequency range between 1.6 and 1.9 THz, which were taken from the Herschel Science Data Archive. Results. We report the first detection of the isotopologues (CCC)-C-13 and (CCC)-C-13. For both species, the ro-vibrational absorption lines Q(2) and Q(4) have been identified, primarily arising from the warm gas physically associated with the strong continuum source, SgrB2(M). From the available CCC ro-vibrational transitions, we derived a gas excitation temperature of T-ex = 44.4(-3.9)(+4.7) K, and a total column density of N(CCC) = 3.88(-0.35)(+0.39) x 10(15) cm(-2). Assuming the excitation temperatures of (CCC)-C-13 and (CCC)-C-13 to be the same as for CCC, we obtained column densities of the C-13-isotopologues of N((CCC)-C-13) = 2.1(-0.6)(+0.9) x 10(14) cm(-2) and N((CCC)-C-13) = 2.4(-0.8)(+1.2) x 10(14) cm(-2). The derived C-12/C-13 abundance ratio in the C-3 molecules is 20.5 +/- 4.2, which is in agreement with the elemental ratio of 20

Context. Carbon molecules and their C-13-isotopologues can be used to determine the C-12/C-13 abundance ratios in stellar and interstellar objects. C-3 is a pure carbon chain molecule found in star-forming regions and in stellar shells of carbon-rich late-type stars. Latest laboratory data of C-13-isotopologues of C-3 allow a selective search for the mono-substituted species (CCC)-C-13 and (CCC)-C-13 based on accurate ro-vibrational frequencies. Aims. We aim to provide the first detection of the C-13-isotopologues (CCC)-C-13 and (CCC)-C-13 in space and to derive the C-12/C-13 ratio of interstellar gas in the massive star-forming region SgrB2(M) near the Galactic Center. Methods. We used the heterodyne receivers GREAT and upGREAT on board SOFIA to search for the ro-vibrational transitions Q(2) and Q(4) of (CCC)-C-13 and (CCC)-C-13 at 1.9 THz along the line of sight towards SgrB2(M). In addition, to determine the local excitation temperature, we analyzed data from nine ro-vibrational transitions of the main isotopologue CCC in the frequency range between 1.6 and 1.9 THz, which were taken from the Herschel Science Data Archive. Results. We report the first detection of the isotopologues (CCC)-C-13 and (CCC)-C-13. For both species, the ro-vibrational absorption lines Q(2) and Q(4) have been identified, primarily arising from the warm gas physically associated with the strong continuum source, SgrB2(M). From the available CCC ro-vibrational transitions, we derived a gas excitation temperature of T-ex = 44.4(-3.9)(+4.7) K, and a total column density of N(CCC) = 3.88(-0.35)(+0.39) x 10(15) cm(-2). Assuming the excitation temperatures of (CCC)-C-13 and (CCC)-C-13 to be the same as for CCC, we obtained column densities of the C-13-isotopologues of N((CCC)-C-13) = 2.1(-0.6)(+0.9) x 10(14) cm(-2) and N((CCC)-C-13) = 2.4(-0.8)(+1.2) x 10(14) cm(-2). The derived C-12/C-13 abundance ratio in the C-3 molecules is 20.5 +/- 4.2, which is in agreement with the elemental ratio of 20

Context. The [CII] 158 mu m far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission.Aims. Our aim is to determine whether the complex profiles observed in [(CII)-C-12] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [(CII)-C-12] and isotopic [(CII)-C-13] line profiles.Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [(CII)-C-13] emission lines, along with the [(CII)-C-12] emission lines, with a high signal-to-noise ratio. We first derived the [(CII)-C-12] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [CII] gas: column density and excitation temperature.Results. We find moderate to high [(CII)-C-12] optical depths in all four sources and self-absorption of [(CII)-C-12] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent A(v) of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent A(v) ranging up to about 13 mag.Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can

Context. The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies.Aims. We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [CII] 158 mu m fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [CII] emission from the Orion Nebula complex at a spatial resolution of 16 and high spectral resolution of 0.2 km s(-1), covering the entire Orion Nebula (M 42) plus M 43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them.Methods. We use [CII] 158 mu m line observations over an area of 1.2 deg(2) in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA.Results. The bubble blown by the O7V star theta (1) Ori C in the Orion Nebula expands rapidly, at 13 km s(-1). Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M 43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6 km s(-1). Comparison with analytical models for the pressure-driven expansion of HII regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5 km s(-1), likely due to the over-pressurized ionized gas as in the case of M 43. We derive an age of 0.4 Myr for this structure.Conclusions. We conclude that the bubble of the Orion Nebula is driven by the mechanica

Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps made with observations using the IRAM 30 m telescope (at 11 '' similar or equal to 4500 AU resolution) and present square-degree (CO)-C-12 and (CO)-C-13 (J = 2-1) maps of the wind-driven Veil bubble that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO globules exist that are blueshifted in velocity with respect to OMC and are embedded in the [CII] 158 mu m-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative local standard of rest velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (R-g = 7100 AU), not massive (M-g = 0.3 M-circle dot), and are moderately dense: n(H) = 4 x 10(4) cm(-3) (median values). They are confined by the external pressure of the shell, P-ext/k greater than or similar to 10(7) cm(-3) K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses (M-g

Context. Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understanding star formation in starbursts (SBs), active galactic nuclei (AGN) phenomena, and the relationship between star formation and AGN activity in galaxies. Analysis of the carbon monoxide ((CO)-C-12) rotational ladder versus the infrared continuum emission (hereafter, (CO)-C-12/IR) in galaxies with different types of activity reveals important differences between them.Aims. We aim to carry out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy using a multi-transition analysis of the spatial distribution of the (CO)-C-12 emission at different spatial scales. We also want to establish the dominant heating mechanism at work in the inner region of this object at smaller spatial scales (less than or similar to 200 pc).Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) (CO)-C-12 line maps and single spectra (from J(up) = 3 to 20) using the Heterodyne Instrument for the Far Infrared (HIFI), the Photoconductor Array Camera and Spectrometer (PACS), and the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, and the Atacama Pathfinder EXperiment (APEX). We combined the (CO)-C-12/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the (CO)-C-12 images to derive the thermal structure of the interstellar medium (ISM) for spatial scales raging from less than or similar to 200 pc to 2 kpc. In addition, we also present single spectra of low- ((CO)-C-12, (CO)-C-13 and [CI]) and high-density (HCN, HNC, HCO+, CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE (NLTE) analyses. Furthermore, the spectral energy distribution of the continuum emission from the FIR to sub-mm wavelengths is also presented.Results. From the NLTE analysis of t

Context. Carbon molecules and their C-13-isotopologues can be used to determine the C-12/C-13 abundance ratios in stellar and interstellar objects. C-3 is a pure carbon chain molecule found in star-forming regions and in stellar shells of carbon-rich late-type stars. Latest laboratory data of C-13-isotopologues of C-3 allow a selective search for the mono-substituted species (CCC)-C-13 and (CCC)-C-13 based on accurate ro-vibrational frequencies. Aims. We aim to provide the first detection of the C-13-isotopologues (CCC)-C-13 and (CCC)-C-13 in space and to derive the C-12/C-13 ratio of interstellar gas in the massive star-forming region SgrB2(M) near the Galactic Center. Methods. We used the heterodyne receivers GREAT and upGREAT on board SOFIA to search for the ro-vibrational transitions Q(2) and Q(4) of (CCC)-C-13 and (CCC)-C-13 at 1.9 THz along the line of sight towards SgrB2(M). In addition, to determine the local excitation temperature, we analyzed data from nine ro-vibrational transitions of the main isotopologue CCC in the frequency range between 1.6 and 1.9 THz, which were taken from the Herschel Science Data Archive. Results. We report the first detection of the isotopologues (CCC)-C-13 and (CCC)-C-13. For both species, the ro-vibrational absorption lines Q(2) and Q(4) have been identified, primarily arising from the warm gas physically associated with the strong continuum source, SgrB2(M). From the available CCC ro-vibrational transitions, we derived a gas excitation temperature of T-ex = 44.4(-3.9)(+4.7) K, and a total column density of N(CCC) = 3.88(-0.35)(+0.39) x 10(15) cm(-2). Assuming the excitation temperatures of (CCC)-C-13 and (CCC)-C-13 to be the same as for CCC, we obtained column densities of the C-13-isotopologues of N((CCC)-C-13) = 2.1(-0.6)(+0.9) x 10(14) cm(-2) and N((CCC)-C-13) = 2.4(-0.8)(+1.2) x 10(14) cm(-2). The derived C-12/C-13 abundance ratio in the C-3 molecules is 20.5 +/- 4.2, which is in agreement with the elemental ratio of 20

Context. The [CII] 158 mu m far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission.Aims. Our aim is to determine whether the complex profiles observed in [(CII)-C-12] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [(CII)-C-12] and isotopic [(CII)-C-13] line profiles.Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [(CII)-C-13] emission lines, along with the [(CII)-C-12] emission lines, with a high signal-to-noise ratio. We first derived the [(CII)-C-12] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [CII] gas: column density and excitation temperature.Results. We find moderate to high [(CII)-C-12] optical depths in all four sources and self-absorption of [(CII)-C-12] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent A(v) of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent A(v) ranging up to about 13 mag.Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can

Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps made with observations using the IRAM 30 m telescope (at 11 '' similar or equal to 4500 AU resolution) and present square-degree (CO)-C-12 and (CO)-C-13 (J = 2-1) maps of the wind-driven Veil bubble that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO globules exist that are blueshifted in velocity with respect to OMC and are embedded in the [CII] 158 mu m-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative local standard of rest velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (R-g = 7100 AU), not massive (M-g = 0.3 M-circle dot), and are moderately dense: n(H) = 4 x 10(4) cm(-3) (median values). They are confined by the external pressure of the shell, P-ext/k greater than or similar to 10(7) cm(-3) K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses (M-g

Context. The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies.Aims. We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [CII] 158 mu m fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [CII] emission from the Orion Nebula complex at a spatial resolution of 16 and high spectral resolution of 0.2 km s(-1), covering the entire Orion Nebula (M 42) plus M 43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them.Methods. We use [CII] 158 mu m line observations over an area of 1.2 deg(2) in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA.Results. The bubble blown by the O7V star theta (1) Ori C in the Orion Nebula expands rapidly, at 13 km s(-1). Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M 43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6 km s(-1). Comparison with analytical models for the pressure-driven expansion of HII regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5 km s(-1), likely due to the over-pressurized ionized gas as in the case of M 43. We derive an age of 0.4 Myr for this structure.Conclusions. We conclude that the bubble of the Orion Nebula is driven by the mechanica

Context. Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understanding star formation in starbursts (SBs), active galactic nuclei (AGN) phenomena, and the relationship between star formation and AGN activity in galaxies. Analysis of the carbon monoxide ((CO)-C-12) rotational ladder versus the infrared continuum emission (hereafter, (CO)-C-12/IR) in galaxies with different types of activity reveals important differences between them.Aims. We aim to carry out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy using a multi-transition analysis of the spatial distribution of the (CO)-C-12 emission at different spatial scales. We also want to establish the dominant heating mechanism at work in the inner region of this object at smaller spatial scales (less than or similar to 200 pc).Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) (CO)-C-12 line maps and single spectra (from J(up) = 3 to 20) using the Heterodyne Instrument for the Far Infrared (HIFI), the Photoconductor Array Camera and Spectrometer (PACS), and the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, and the Atacama Pathfinder EXperiment (APEX). We combined the (CO)-C-12/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the (CO)-C-12 images to derive the thermal structure of the interstellar medium (ISM) for spatial scales raging from less than or similar to 200 pc to 2 kpc. In addition, we also present single spectra of low- ((CO)-C-12, (CO)-C-13 and [CI]) and high-density (HCN, HNC, HCO+, CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE (NLTE) analyses. Furthermore, the spectral energy distribution of the continuum emission from the FIR to sub-mm wavelengths is also presented.Results. From the NLTE analysis of t

Aims. We study the spatial distribution and kinematics of water emission in a similar to 8 x 8 pc(2) region of the Galactic center (GC) that covers the main molecular features around the supermassive black hole Sagittarius A* (Sgr A*). We also analyze the water excitation to derive the physical conditions and water abundances in the circumnuclear disk (CND) and the quiescent clouds. Methods. We presented the integrated line intensity maps of the ortho 1(10) - 1(01), and para 2(02) - 1(11) and 1(11) - 0(00) water transitions observed using the On the Fly mapping mode with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. To study the water excitation, we used HIFI observations of the ground state ortho and para (H2O)-O-18 transitions toward three selected positions in the vicinity of Sgr A*. In our study, we also used dust continuum measurements of the CND, obtained with the Spectral and Photometric Imaging REceiver (SPIRE) instrument. Using a non-local thermodynamical equilibrium (LTE) radiative transfer code, the water line profiles and dust continuum were modeled, deriving H2O abundances (XH2O), turbulent velocities (V-t), and dust temperatures (T-d). We also used a rotating ring model to reproduce the CND kinematics represented by the position velocity (PV) diagram derived from para 2(02) - 1(11) H2O lines. Results. In our H2O maps we identify the emission associated with known features around Sgr A*: CND, the Western Streamer, and the 20 and 50 km s(-1) clouds. The ground-state ortho water maps show absorption structures in the velocity range of [-220,10] km s 1 associated with foreground sources. The PV diagram reveals that the 2(02) - 1(11) H2O emission traces the CND also observed in other high-dipole molecules such as SiO, HCN, and CN. Using the non-LTE code, we derive high XH2O of similar to (0.1-1.3) x 10(-5), V-t of 14-23 km s(-1), and T-d of 15-45 K for the CND, and the lower XH2O of 4 x 10(-8) and V-t of 9 km s(-1) for the 20 km s

Aims. We study the spatial distribution and kinematics of water emission in a similar to 8 x 8 pc(2) region of the Galactic center (GC) that covers the main molecular features around the supermassive black hole Sagittarius A* (Sgr A*). We also analyze the water excitation to derive the physical conditions and water abundances in the circumnuclear disk (CND) and the quiescent clouds. Methods. We presented the integrated line intensity maps of the ortho 1(10) - 1(01), and para 2(02) - 1(11) and 1(11) - 0(00) water transitions observed using the On the Fly mapping mode with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. To study the water excitation, we used HIFI observations of the ground state ortho and para (H2O)-O-18 transitions toward three selected positions in the vicinity of Sgr A*. In our study, we also used dust continuum measurements of the CND, obtained with the Spectral and Photometric Imaging REceiver (SPIRE) instrument. Using a non-local thermodynamical equilibrium (LTE) radiative transfer code, the water line profiles and dust continuum were modeled, deriving H2O abundances (XH2O), turbulent velocities (V-t), and dust temperatures (T-d). We also used a rotating ring model to reproduce the CND kinematics represented by the position velocity (PV) diagram derived from para 2(02) - 1(11) H2O lines. Results. In our H2O maps we identify the emission associated with known features around Sgr A*: CND, the Western Streamer, and the 20 and 50 km s(-1) clouds. The ground-state ortho water maps show absorption structures in the velocity range of [-220,10] km s 1 associated with foreground sources. The PV diagram reveals that the 2(02) - 1(11) H2O emission traces the CND also observed in other high-dipole molecules such as SiO, HCN, and CN. Using the non-LTE code, we derive high XH2O of similar to (0.1-1.3) x 10(-5), V-t of 14-23 km s(-1), and T-d of 15-45 K for the CND, and the lower XH2O of 4 x 10(-8) and V-t of 9 km s(-1) for the 20 km s

The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H-2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H-2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a canonical CH abundance needs to be addressed. Methods. The N = 2 <- 1 ground state transition of CH at lambda 149 mu m has become accessible to high-resolution spectroscopy thanks to the German Receiver for Astronomy at Terahertz Frequencies (GREAT) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at lambda 560 mu m, environments forming massive stars can be analyzed. For this we present a case study on the proto-Trapezium cluster W3 IRS5. Results. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-mill

The central area (40 x 40) of the bipolar nebula S106 was mapped in the [O I] line at 63.2 mu m (4.74 THz) with high angular (6) and spectral (0.24 MHz) resolution, using the GREAT heterodyne receiver on board SOFIA. The spatial and spectral emission distribution of [01] is compared to emission in the CO 16 -> 15, [C II] 158 mu m, and CO 11 -> 10 lines, mm-molecular lines, and continuum. The [01] emission is composed of several velocity components in the range from -30 to 25 km s(-1). The high-velocity blue and red-shifted emission (v = 30 to 9 km s(-1) and 8 to 25 km s(-1)) can be explained as arising from accelerated photodissociated gas associated with a dark lane close to the massive binary system S106 IR, and from shocks caused by the stellar wind and/or a disk envelope interaction. At velocities from 9 to 4 km s(-1) and from 0.5 to 8 km s(-1) line wings are observed in most of the lines that we attribute to cooling in photodissociation regions (PDRs) created by the ionizing radiation impinging on the cavity walls. The velocity range from -4 to 0.5 km s(-1) is dominated by emission from the clumpy molecular cloud, and the [O I], [C II], and high-J CO lines are excited in PDRs on clump surfaces that are illuminated by the central stars. Modelling the line emission in the different velocity ranges with the KOSMA-tau code constrains a radiation field chi of a few times 10(4) and densities n of a few times 10(4) cm(-3). Considering self-absorption of the [01] line results in higher densities (up to 106 cm 3) only for the gas component seen at high blue and red velocities. We thus confirm the scenario found in other studies that the emission of these lines can be explained by a two-phase PDR, but attribute the high-density gas to the high -velocity component only. The dark lane has a mass of similar to 275 M-circle dot and shows a velocity difference of similar to 1.4 km s(-1) along its projected length of similar to 1 pc, determined from (HCO+)-C-13 1 -> 0 mapping.

The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H-2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H-2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a canonical CH abundance needs to be addressed. Methods. The N = 2 <- 1 ground state transition of CH at lambda 149 mu m has become accessible to high-resolution spectroscopy thanks to the German Receiver for Astronomy at Terahertz Frequencies (GREAT) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at lambda 560 mu m, environments forming massive stars can be analyzed. For this we present a case study on the proto-Trapezium cluster W3 IRS5. Results. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-mill

The central area (40 x 40) of the bipolar nebula S106 was mapped in the [O I] line at 63.2 mu m (4.74 THz) with high angular (6) and spectral (0.24 MHz) resolution, using the GREAT heterodyne receiver on board SOFIA. The spatial and spectral emission distribution of [01] is compared to emission in the CO 16 -> 15, [C II] 158 mu m, and CO 11 -> 10 lines, mm-molecular lines, and continuum. The [01] emission is composed of several velocity components in the range from -30 to 25 km s(-1). The high-velocity blue and red-shifted emission (v = 30 to 9 km s(-1) and 8 to 25 km s(-1)) can be explained as arising from accelerated photodissociated gas associated with a dark lane close to the massive binary system S106 IR, and from shocks caused by the stellar wind and/or a disk envelope interaction. At velocities from 9 to 4 km s(-1) and from 0.5 to 8 km s(-1) line wings are observed in most of the lines that we attribute to cooling in photodissociation regions (PDRs) created by the ionizing radiation impinging on the cavity walls. The velocity range from -4 to 0.5 km s(-1) is dominated by emission from the clumpy molecular cloud, and the [O I], [C II], and high-J CO lines are excited in PDRs on clump surfaces that are illuminated by the central stars. Modelling the line emission in the different velocity ranges with the KOSMA-tau code constrains a radiation field chi of a few times 10(4) and densities n of a few times 10(4) cm(-3). Considering self-absorption of the [01] line results in higher densities (up to 106 cm 3) only for the gas component seen at high blue and red velocities. We thus confirm the scenario found in other studies that the emission of these lines can be explained by a two-phase PDR, but attribute the high-density gas to the high -velocity component only. The dark lane has a mass of similar to 275 M-circle dot and shows a velocity difference of similar to 1.4 km s(-1) along its projected length of similar to 1 pc, determined from (HCO+)-C-13 1 -> 0 mapping.

Context. Photon dominated regions (PDRs) are interfaces between the mainly ionized and mainly molecular material around young massive stars. Analysis of the physical and chemical structure of such regions traces the impact of far-ultraviolet radiation of young massive stars on their environment. Aims. We present results on the physical and chemical structure of the prototypical high UV-illumination edge-on Orion Bar PDR from an unbiased spectral line survey with a wide spectral coverage which includes lines of many important gas coolants such as [CII], [CI], and CO and other key molecules such as H2CO, H2O, HCN, HCO+, and SO. Methods. A spectral scan from 480-1250 GHz and 1410-1910 GHz at 1.1 MHz resolution was obtained by the HIFI instrument on board the Herschel Space Observatory. We obtained physical parameters for the observed molecules. For molecules with multiple transitions we used rotational diagrams to obtain excitation temperatures and column densities. For species with a single detected transition we used an optically thin LTE approximation. In the case of species with available collisional rates, we also performed a non-LTE analysis to obtain kinetic temperatures, H-2 volume densities, and column densities. Results. About 120 lines corresponding to 29 molecules (including isotopologues) have been detected in the Herschel/HIFI line survey, including 11 transitions of CO, 7 transitions of (CO)-C-13, 6 transitions of (CO)-O-18, 10 transitions of H2CO, and 6 transitions of H2O. The rotational temperatures are in the range between similar to 22 and similar to 146 K and the column densities are in the range between 1.8 x 10(12) cm(-2) and 4.5 x 10(17) cm(-2). For species with at least three detected transitions and available collisional excitation rates we derived a best fit kinetic temperature and H-2 volume density. Most species trace kinetic temperatures in the range between 100 and 150 K and H-2 volume densities in the range between 10(5) and 10(6) cm(-3).

The physical state of the gas in the central 500 pc of NGC 5128 (the radio galaxy Centaurus A), was investigated using the finestructure lines of carbon [C I], [C II]; oxygen [O I], [O III], and nitrogen [N II], [N III] as well as the 12CO(4 3) molecular line. The circumnuclear disk (CND) is traced by emission from dust and the neutral gas ([C I] and 12CO). A gas outflow with a line-of-sight velocity of 60 km s(-1) is evident in both lines. The [C I] emission from the CND is unusually strong with respect to that from CO. The center of the CND (R < 90 pc) is bright in [O I], [O III], and [C II]; [O I] lambda 63 mu m emission dominates that of [C II] even though it is absorbed with optical depths tau = 1.0-1.5. The outflow is well- traced by the [N II] and [N III] lines and also seen in the [C II] and [O III] lines that peak in the center. Ionized gas densities are highest in the CND (about 100 cm 3) and low everywhere else. Neutral gas densities range from 4000 cm 3 (outflow, extended thin disk ETD) to 20 000 cm 3 (CND). The CND radiation field (Go approximate to 4) is weak compared to the ETD starburst field (Go approximate to 40). The outflow has a much stronger radiation field (Go = 130). The total mass of all the CND gas is 9 .1 +/- 0.9 x10(7) M-circle dot but the mass of the outflowing gas is only 15-30% of that. The outflow most likely originates from the shock-dominated CND cavity surrounding the central black hole. With a factor of three uncertainty, the mass outflow rate is approximate to 2 M-circle dot yr 1, a thousand times higher than the accretion rate of the black hole. Without replenishment, the CND will be depleted in 15-120million years. However, the outflow velocity is well below the escape velocity.

We present SOFIA/GREAT [C II] P-2(3/2) -> P-2(1/2) (1.9005369 THz) observations of nearby clouds near the lines of sight towards the quasars B0355+508 and B0212+735. These clouds have previously been identified as warm non-LTE diffuse clouds with a temperature of T greater than or similar to 30 K and sub-thermally excited CO lines. They are highly structured in CO with small-scale bright spots (I(CO J = 1-0) similar to 5-20 Kkm s(-1)), both spectrally and spatially. This small-scale structure has been interpreted as small-scale variations in the chemistry, not as density and column-density structure. We did not detect [C II] 158 mu m emission within the rms noise of similar to 0.1-0.3 K. Our non-detection in [C II] contradicts the above scenario. In diffuse clouds, the efficiency of photo-electric heating is highest. Under the assumption that [C II] is the dominant coolant in diffuse clouds, we can calculate the predicted [C II] emission arising from these clouds. Based on the derived hydrogen column densities for the diffuse clouds, a line width in [C II] of similar order to that of CO, and when at least the minimum amount of heating in the clouds is due to cosmic-ray heating, [C II] line intensities greater than or similar to 1.5 to 5 Kkm s(-1) are expected, which is a factor similar to 3 to 15 above the upper limits of the observations. The upper limits of the [C II] and the observed CO line intensities are, however, consistent with the intensities predicted for photon-dominated region (PDR) surfaces on regular cold (T similar to 15 K) low-density cloud fragments. Lower temperatures lead to less excited [C II]. The assumption of lower densities, which would equally lower the [C II] excitation, contradicts the observed cloud sizes and column densities. The CO(2-1)/CO(1-0) line ratios observed in these clouds are consistent with cloud temperatures of T similar to 15 K. The KOSMA-tau PDR-model of a cold moderate-density clump or an ensemble of such clumps with a can

Context. Photon dominated regions (PDRs) are interfaces between the mainly ionized and mainly molecular material around young massive stars. Analysis of the physical and chemical structure of such regions traces the impact of far-ultraviolet radiation of young massive stars on their environment. Aims. We present results on the physical and chemical structure of the prototypical high UV-illumination edge-on Orion Bar PDR from an unbiased spectral line survey with a wide spectral coverage which includes lines of many important gas coolants such as [CII], [CI], and CO and other key molecules such as H2CO, H2O, HCN, HCO+, and SO. Methods. A spectral scan from 480-1250 GHz and 1410-1910 GHz at 1.1 MHz resolution was obtained by the HIFI instrument on board the Herschel Space Observatory. We obtained physical parameters for the observed molecules. For molecules with multiple transitions we used rotational diagrams to obtain excitation temperatures and column densities. For species with a single detected transition we used an optically thin LTE approximation. In the case of species with available collisional rates, we also performed a non-LTE analysis to obtain kinetic temperatures, H-2 volume densities, and column densities. Results. About 120 lines corresponding to 29 molecules (including isotopologues) have been detected in the Herschel/HIFI line survey, including 11 transitions of CO, 7 transitions of (CO)-C-13, 6 transitions of (CO)-O-18, 10 transitions of H2CO, and 6 transitions of H2O. The rotational temperatures are in the range between similar to 22 and similar to 146 K and the column densities are in the range between 1.8 x 10(12) cm(-2) and 4.5 x 10(17) cm(-2). For species with at least three detected transitions and available collisional excitation rates we derived a best fit kinetic temperature and H-2 volume density. Most species trace kinetic temperatures in the range between 100 and 150 K and H-2 volume densities in the range between 10(5) and 10(6) cm(-3).

We present SOFIA/GREAT [C II] P-2(3/2) -> P-2(1/2) (1.9005369 THz) observations of nearby clouds near the lines of sight towards the quasars B0355+508 and B0212+735. These clouds have previously been identified as warm non-LTE diffuse clouds with a temperature of T greater than or similar to 30 K and sub-thermally excited CO lines. They are highly structured in CO with small-scale bright spots (I(CO J = 1-0) similar to 5-20 Kkm s(-1)), both spectrally and spatially. This small-scale structure has been interpreted as small-scale variations in the chemistry, not as density and column-density structure. We did not detect [C II] 158 mu m emission within the rms noise of similar to 0.1-0.3 K. Our non-detection in [C II] contradicts the above scenario. In diffuse clouds, the efficiency of photo-electric heating is highest. Under the assumption that [C II] is the dominant coolant in diffuse clouds, we can calculate the predicted [C II] emission arising from these clouds. Based on the derived hydrogen column densities for the diffuse clouds, a line width in [C II] of similar order to that of CO, and when at least the minimum amount of heating in the clouds is due to cosmic-ray heating, [C II] line intensities greater than or similar to 1.5 to 5 Kkm s(-1) are expected, which is a factor similar to 3 to 15 above the upper limits of the observations. The upper limits of the [C II] and the observed CO line intensities are, however, consistent with the intensities predicted for photon-dominated region (PDR) surfaces on regular cold (T similar to 15 K) low-density cloud fragments. Lower temperatures lead to less excited [C II]. The assumption of lower densities, which would equally lower the [C II] excitation, contradicts the observed cloud sizes and column densities. The CO(2-1)/CO(1-0) line ratios observed in these clouds are consistent with cloud temperatures of T similar to 15 K. The KOSMA-tau PDR-model of a cold moderate-density clump or an ensemble of such clumps with a can

The physical state of the gas in the central 500 pc of NGC 5128 (the radio galaxy Centaurus A), was investigated using the finestructure lines of carbon [C I], [C II]; oxygen [O I], [O III], and nitrogen [N II], [N III] as well as the 12CO(4 3) molecular line. The circumnuclear disk (CND) is traced by emission from dust and the neutral gas ([C I] and 12CO). A gas outflow with a line-of-sight velocity of 60 km s(-1) is evident in both lines. The [C I] emission from the CND is unusually strong with respect to that from CO. The center of the CND (R < 90 pc) is bright in [O I], [O III], and [C II]; [O I] lambda 63 mu m emission dominates that of [C II] even though it is absorbed with optical depths tau = 1.0-1.5. The outflow is well- traced by the [N II] and [N III] lines and also seen in the [C II] and [O III] lines that peak in the center. Ionized gas densities are highest in the CND (about 100 cm 3) and low everywhere else. Neutral gas densities range from 4000 cm 3 (outflow, extended thin disk ETD) to 20 000 cm 3 (CND). The CND radiation field (Go approximate to 4) is weak compared to the ETD starburst field (Go approximate to 40). The outflow has a much stronger radiation field (Go = 130). The total mass of all the CND gas is 9 .1 +/- 0.9 x10(7) M-circle dot but the mass of the outflowing gas is only 15-30% of that. The outflow most likely originates from the shock-dominated CND cavity surrounding the central black hole. With a factor of three uncertainty, the mass outflow rate is approximate to 2 M-circle dot yr 1, a thousand times higher than the accretion rate of the black hole. Without replenishment, the CND will be depleted in 15-120million years. However, the outflow velocity is well below the escape velocity.

Context. The chemistry of the diffuse interstellar medium rests upon three pillars: exothermic ion-neutral reactions (cold chemistry), endothermic neutral-neutral reactions with significant activation barriers (warm chemistry), and reactions on the surfaces of dust grains. While warm chemistry becomes important in the shocks associated with turbulent dissipation regions, the main path for the formation of interstellar OH and H2O is that of cold chemistry. Aims. The aim of this study is to observationally confirm the association of atomic oxygen with both atomic and molecular gas phases, and to understand the measured abundances of OH and OH+ as a function of the available reservoir of H-2. Methods. We obtained absorption spectra of the ground states of OH, OH+ and OI with high-velocity resolution, with GREAT onboard SOFIA, and with the THz receiver at the APEX. We analyzed them along with ancillary spectra of HF and CH from HIFI. To deconvolve them from the hyperfine structure and to separate the blend that is due to various velocity components on the sightline, we fit model spectra consisting of an appropriate number of Gaussian profiles using a method combining simulated annealing with downhill simplex minimization. Together with HF and/or CH as a surrogate for H-2, and HI lambda 21 cm data, the molecular hydrogen fraction f(H2)(N) = N(H-2)/(N(H) + 2N(H-2)) can be determined. We then investigated abundance ratios as a function of f(H2)(N). Results. The column density of OI is correlated at a high significance with the amount of available molecular and atomic hydrogen, with an atomic oxygen abundance of 3 x 10(-4) relative to H nuclei. While the velocities of the absorption features of OH and OH+ are loosely correlated and reflect the spiral arm crossings on the sightline, upon closer inspection they display an anticorrespondence. The arm-to-interarm density contrast is found to be higher in OH than in OH+. While both species can coexist, with a higher abundance in

This paper presents [C II], [C I] and CO emission line maps of the star-forming regions N 66, N 25+N 26, and N 88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large H II region N 66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC 346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N 25+N 26 and N 88 maps, diffuse [C II] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the H II regions. In all regions, the distribution of this bright [C II] emission and the less prominent [C I] emission closely follows the outline of the CO complexes, but the intensity of the [C II] and [C I] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [C II] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [C II] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [C II] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with [C II] rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [C II] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed.

Aims. We investigate the spatial and spectral distribution of the local standard of rest (LSR) velocity resolved submillimetre emission from the warm (25-90 K) gas in the Sgr A Complex, located in the Galactic centre. Methods. We present large-scale submillimetre heterodyne observations towards the Sgr A Complex covering similar to 300 arcmin(2). These data were obtained in the frame of the Herschel EXtraGALactic guaranteed time key program (HEXGAL) with the Herschel-HIFI satellite and are complemented with submillimetre observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(J = 4-3) at 461.0 GHz observed with the NANTEN2/SMART telescope, and [CI] P-3(1)-P-3(0) at 492.2 GHz, [CI] P-3(2)-P-3(1) at 809.3 GHz, [NII] P-3(1)-P-3(0) at 1461.1 GHz, and [CII] P-2(3/2)-P-2(1/2) at 1900.5 GHz observed with the Herschel-HIFI satellite. The observations are presented in a 1 kms(-1) spectral resolution and a spatial resolution ranging from 46 arcsec to 28 arcsec. The spectral coverage of the three lower frequency lines is +/- 200 km s(-1), while in the two high frequency lines, the upper LSR velocity limit is +94 km s(-1) and + 145 km s(-1) for the [NII] and [CII] lines, respectively. Results. The spatial distribution of the emission in all lines is very widespread. The bulk of the carbon monoxide emission is found towards Galactic latitudes below the Galactic plane, and all the known molecular clouds are identified. Both neutral atomic carbon lines have their brightest emission associated with the +50 km s(-1) cloud. Their spatial distribution at this LSR velocity describes a crescent-shape structure, which is probably the result of interaction with the energetic event (one or several supernovae explosions) that gave origin to the non-thermal Sgr A-East source. The [CII] and [NII] emissions have most of their flux associated with the thermal arched-filaments and the H region and bright spots i

Context. Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 mu m line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs but can also originate from the ionized gas closely surrounding young massive stars. The proportion of the [C II] emission from HII regions relative to that from PDRs can vary significantly. Aims. We investigate the question of how much of the [C II] emission in the nucleus of the nearby spiral galaxy IC 342 is contributed by PDRs and by the ionized gas. We examine the spatial variations of starburst/PDR activity and study the correlation of the [C II] line with the [N II] 205 mu m emission line coming exclusively from the HII regions. Methods. We present small maps of [C II] 158 mu m and [N II] 205 mu m lines recently observed with the GREAT receiver on board SOFIA. We present different methods to utilize the superior spatial and spectral resolution of our new data to infer information on how the gas kinematics in the nuclear region influence the observed line profiles. In particular we present a super-resolution method to derive how unresolved, kinematically correlated structures in the beam contribute to the observed line shapes. Results. We find that the emission coming from the ionized gas shows a kinematic component in addition to the general Doppler signature of the molecular gas. We interpret this as the signature of two bi-polar lobes of ionized gas expanding out of the galactic plane. We then show how this requires an adaptation of our understanding of the geometrical structure of the nucleus of IC 342. Examining the starburst activity we find ratios I([C II]) = I((CO)-C-12(1-0)) between 400 and 1800 in energy units. Applying predictions from numerical models of HII and PDR regions to derive the contribution from the ionized phase to the total [C II] emission we find that 35-90% of the observed [C II] inten

We present a new multi-pixel high resolution (R greater than or similar to 10(7)) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 x 7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8-2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the [CII] line at 1.9 THz in 2015 and extended to 1.83-2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA's instrument suite already for ongoing observing cycle 4.

Context. The chemistry of the diffuse interstellar medium rests upon three pillars: exothermic ion-neutral reactions (cold chemistry), endothermic neutral-neutral reactions with significant activation barriers (warm chemistry), and reactions on the surfaces of dust grains. While warm chemistry becomes important in the shocks associated with turbulent dissipation regions, the main path for the formation of interstellar OH and H2O is that of cold chemistry. Aims. The aim of this study is to observationally confirm the association of atomic oxygen with both atomic and molecular gas phases, and to understand the measured abundances of OH and OH+ as a function of the available reservoir of H-2. Methods. We obtained absorption spectra of the ground states of OH, OH+ and OI with high-velocity resolution, with GREAT onboard SOFIA, and with the THz receiver at the APEX. We analyzed them along with ancillary spectra of HF and CH from HIFI. To deconvolve them from the hyperfine structure and to separate the blend that is due to various velocity components on the sightline, we fit model spectra consisting of an appropriate number of Gaussian profiles using a method combining simulated annealing with downhill simplex minimization. Together with HF and/or CH as a surrogate for H-2, and HI lambda 21 cm data, the molecular hydrogen fraction f(H2)(N) = N(H-2)/(N(H) + 2N(H-2)) can be determined. We then investigated abundance ratios as a function of f(H2)(N). Results. The column density of OI is correlated at a high significance with the amount of available molecular and atomic hydrogen, with an atomic oxygen abundance of 3 x 10(-4) relative to H nuclei. While the velocities of the absorption features of OH and OH+ are loosely correlated and reflect the spiral arm crossings on the sightline, upon closer inspection they display an anticorrespondence. The arm-to-interarm density contrast is found to be higher in OH than in OH+. While both species can coexist, with a higher abundance in

Aims. We investigate the spatial and spectral distribution of the local standard of rest (LSR) velocity resolved submillimetre emission from the warm (25-90 K) gas in the Sgr A Complex, located in the Galactic centre. Methods. We present large-scale submillimetre heterodyne observations towards the Sgr A Complex covering similar to 300 arcmin(2). These data were obtained in the frame of the Herschel EXtraGALactic guaranteed time key program (HEXGAL) with the Herschel-HIFI satellite and are complemented with submillimetre observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(J = 4-3) at 461.0 GHz observed with the NANTEN2/SMART telescope, and [CI] P-3(1)-P-3(0) at 492.2 GHz, [CI] P-3(2)-P-3(1) at 809.3 GHz, [NII] P-3(1)-P-3(0) at 1461.1 GHz, and [CII] P-2(3/2)-P-2(1/2) at 1900.5 GHz observed with the Herschel-HIFI satellite. The observations are presented in a 1 kms(-1) spectral resolution and a spatial resolution ranging from 46 arcsec to 28 arcsec. The spectral coverage of the three lower frequency lines is +/- 200 km s(-1), while in the two high frequency lines, the upper LSR velocity limit is +94 km s(-1) and + 145 km s(-1) for the [NII] and [CII] lines, respectively. Results. The spatial distribution of the emission in all lines is very widespread. The bulk of the carbon monoxide emission is found towards Galactic latitudes below the Galactic plane, and all the known molecular clouds are identified. Both neutral atomic carbon lines have their brightest emission associated with the +50 km s(-1) cloud. Their spatial distribution at this LSR velocity describes a crescent-shape structure, which is probably the result of interaction with the energetic event (one or several supernovae explosions) that gave origin to the non-thermal Sgr A-East source. The [CII] and [NII] emissions have most of their flux associated with the thermal arched-filaments and the H region and bright spots i

This paper presents [C II], [C I] and CO emission line maps of the star-forming regions N 66, N 25+N 26, and N 88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large H II region N 66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC 346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N 25+N 26 and N 88 maps, diffuse [C II] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the H II regions. In all regions, the distribution of this bright [C II] emission and the less prominent [C I] emission closely follows the outline of the CO complexes, but the intensity of the [C II] and [C I] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [C II] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [C II] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [C II] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with [C II] rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [C II] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed.

Context. Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 mu m line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs but can also originate from the ionized gas closely surrounding young massive stars. The proportion of the [C II] emission from HII regions relative to that from PDRs can vary significantly. Aims. We investigate the question of how much of the [C II] emission in the nucleus of the nearby spiral galaxy IC 342 is contributed by PDRs and by the ionized gas. We examine the spatial variations of starburst/PDR activity and study the correlation of the [C II] line with the [N II] 205 mu m emission line coming exclusively from the HII regions. Methods. We present small maps of [C II] 158 mu m and [N II] 205 mu m lines recently observed with the GREAT receiver on board SOFIA. We present different methods to utilize the superior spatial and spectral resolution of our new data to infer information on how the gas kinematics in the nuclear region influence the observed line profiles. In particular we present a super-resolution method to derive how unresolved, kinematically correlated structures in the beam contribute to the observed line shapes. Results. We find that the emission coming from the ionized gas shows a kinematic component in addition to the general Doppler signature of the molecular gas. We interpret this as the signature of two bi-polar lobes of ionized gas expanding out of the galactic plane. We then show how this requires an adaptation of our understanding of the geometrical structure of the nucleus of IC 342. Examining the starburst activity we find ratios I([C II]) = I((CO)-C-12(1-0)) between 400 and 1800 in energy units. Applying predictions from numerical models of HII and PDR regions to derive the contribution from the ionized phase to the total [C II] emission we find that 35-90% of the observed [C II] inten

We present a new multi-pixel high resolution (R greater than or similar to 10(7)) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 x 7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8-2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the [CII] line at 1.9 THz in 2015 and extended to 1.83-2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA's instrument suite already for ongoing observing cycle 4.

Context. The [C II] 158 mu m line is one of the dominant coolants of the ISM, and an important probe with which to study the star formation process. Recent Herschel/HIFI and SOFIA/GREAT observations showed that assuming the total velocity-integrated intensity of this line is directly associated with the star-forming material is inadequate. Aims. We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-J CO lines toward the star-forming region M17 SW. Methods. We mapped a 4.1 pc x 4.7 pc region in the [C I] 609 mu m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30 m telescope. Because of the velocity-resolved spectra, we analyze the data based on velocity channel maps that are 1 km s(-1) wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. Results. The distribution of the emission from the isotopologues (CO)-C-13, (CO)-O-17, and (CO)-O-18 resembles more closely that of the [C I] emission than that of the (CO)-C-12 emission. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km s(-1)) velocity channels. Conclusions. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Excitation temperatures up to 200 K are found along the ridge. Column densities in 1 km s(-1) channels between similar to 10(15) cm(-2) and similar to 10(17) cm-2 were found for [C I]. Just similar to 20 % of the velocity range (similar to 40 km s(-1)) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total (

Context. The [C II] 158 mu m line is one of the dominant coolants of the ISM, and an important probe with which to study the star formation process. Recent Herschel/HIFI and SOFIA/GREAT observations showed that assuming the total velocity-integrated intensity of this line is directly associated with the star-forming material is inadequate. Aims. We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-J CO lines toward the star-forming region M17 SW. Methods. We mapped a 4.1 pc x 4.7 pc region in the [C I] 609 mu m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30 m telescope. Because of the velocity-resolved spectra, we analyze the data based on velocity channel maps that are 1 km s(-1) wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. Results. The distribution of the emission from the isotopologues (CO)-C-13, (CO)-O-17, and (CO)-O-18 resembles more closely that of the [C I] emission than that of the (CO)-C-12 emission. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km s(-1)) velocity channels. Conclusions. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Excitation temperatures up to 200 K are found along the ridge. Column densities in 1 km s(-1) channels between similar to 10(15) cm(-2) and similar to 10(17) cm-2 were found for [C I]. Just similar to 20 % of the velocity range (similar to 40 km s(-1)) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total (

Context. Stars are formed in dense molecular clouds. These dense clouds experience radiative feedback from UV photons, and X-ray from stars, embedded prestellar cores, young stellar objects (YSOs), and ultra compact H II regions. This radiative feedback affects the chemistry and thermodynamics of the gas. Aims. We aim to probe the chemical and energetic conditions created by radiative feedback through observations of multiple CO, HCN, and HCO+ transitions. We measure the spatial distribution and excitation of the dense gas (n(H-2) > 10(4) cm(-3)) in the core region of M17 SW and aim to investigate the influence of UV radiation fields. Methods. We used the dual band receiver GREAT on board the SOFIA airborne telescope to obtain a 5.'7 x 3.'7 map of the J = 16 -> 15, J = 12 -> 11, and J = 11 -> 10 transitions of (CO)-C-12 in M17 SW. We compare these maps with corresponding APEX and IRAM 30m telescope data for low-and mid-J CO, HCN, and HCO+ emission lines, including maps of the HCN J = 8 -> 7 and HCO+ J = 9 -> 8 transitions. The excitation conditions of (CO)-C-12, HCO+, and HCN are estimated with a two-phase non-LTE radiative transfer model of the line spectral energy distributions (LSEDs) at four selected positions. The energy balance at these positions is also studied. Results. We obtained extensive LSEDs for the CO, HCN, and HCO+ molecules toward M17 SW. These LSEDs can be fit simultaneously using the same density and temperature in the two-phase models and to the spectra of all three molecules over a similar to 12 square arc minute size region of M17 SW. Temperatures of up to 240 K are found toward the position of the peak emission of the (CO)-C-12 J = 16 -> 15 line. High densities of 10(6) cm(-3) were found at the position of the peak HCN J = 8 -> 7 emission. Conclusions. We found HCO+/HCN line ratios larger than unity, which can be explained by a lower excitation temperature of the higher-J HCN lines. The LSED shape, particularly the high-J tail of the CO lines

Context. The [C II] 158 mu m line is one of the dominant coolants of the ISM, and an important probe with which to study the star formation process. Recent Herschel/HIFI and SOFIA/GREAT observations showed that assuming the total velocity-integrated intensity of this line is directly associated with the star-forming material is inadequate. Aims. We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-J CO lines toward the star-forming region M17 SW. Methods. We mapped a 4.1 pc x 4.7 pc region in the [C I] 609 mu m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30 m telescope. Because of the velocity-resolved spectra, we analyze the data based on velocity channel maps that are 1 km s(-1) wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. Results. The distribution of the emission from the isotopologues (CO)-C-13, (CO)-O-17, and (CO)-O-18 resembles more closely that of the [C I] emission than that of the (CO)-C-12 emission. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km s(-1)) velocity channels. Conclusions. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Excitation temperatures up to 200 K are found along the ridge. Column densities in 1 km s(-1) channels between similar to 10(15) cm(-2) and similar to 10(17) cm-2 were found for [C I]. Just similar to 20 % of the velocity range (similar to 40 km s(-1)) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total (

Context. The [C II] 158 mu m line is one of the dominant coolants of the ISM, and an important probe with which to study the star formation process. Recent Herschel/HIFI and SOFIA/GREAT observations showed that assuming the total velocity-integrated intensity of this line is directly associated with the star-forming material is inadequate. Aims. We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-J CO lines toward the star-forming region M17 SW. Methods. We mapped a 4.1 pc x 4.7 pc region in the [C I] 609 mu m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30 m telescope. Because of the velocity-resolved spectra, we analyze the data based on velocity channel maps that are 1 km s(-1) wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. Results. The distribution of the emission from the isotopologues (CO)-C-13, (CO)-O-17, and (CO)-O-18 resembles more closely that of the [C I] emission than that of the (CO)-C-12 emission. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km s(-1)) velocity channels. Conclusions. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Excitation temperatures up to 200 K are found along the ridge. Column densities in 1 km s(-1) channels between similar to 10(15) cm(-2) and similar to 10(17) cm-2 were found for [C I]. Just similar to 20 % of the velocity range (similar to 40 km s(-1)) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total (