Search

We report SOFIA/GREAT observations of high-J CO lines and [C ii] observations of the super star cluster candidate H72.97-69.39 in the Large Magellanic Cloud (LMC), which is in its very early formation stage. We use our observations to determine if shocks are heating the gas or if photon-dominated regions (PDRs) are being heated by local far-UV radiation. We use a PDR model and a shock model to determine whether the CO and [C ii] lines arise from PDRs or shocks. We can reproduce the observed high-J CO and [C ii] emission with a clumpy PDR model with the following properties: a density of 10(4.7) cm(-3), a mass of 10(4) M, and UV radiation of 10(3.5) in units of Draine field. Comparison with the ALMA beam-filling factor suggests a higher density within the uncertainty of the fit. We find the lower-limit [C ii]/total infrared (TIR) ratio (epsilon) traced by [C ii]/TIR to be 0.026%, lower than other known young star-forming regions in the LMC. Our shock models may explain the CO (16-15) and CO (11-10) emission lines with shock velocity of 8-11 km s(-1), pre-shock density of 10(4)-10(5) cm(-3), and G(UV) = 0 in units of Draine field. However, the [C ii] line emission cannot be explained by a shock model, thus it is originating in a different gas component. Observations of [O i] 63 mu m predicted to be 1.1 x 10(-13) W m(-2) by PDR models and 7.8 x 10(-15) W m(-2) by shock models will help distinguish between the PDR and shock scenarios.

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. 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

We present SOFIA/FIFI-LS observations of the [C II] 158 mu m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H I data to compare [C II] emission to dust properties, star formation rate (SFR), H-2, and H I at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the [C II] luminosity to arms, and 19% and 8% to the center and interarm region, respectively. [C II]/TIR, [C II]/CO, and [C II]/PAH radial profiles are largely constant, but rise at large radii (greater than or similar to 8 kpc) and drop in the center ([C II] deficit). This increase at large radii and the observed decline with the 70 mu m/100 mu m dust color are likely driven by radiation field hardness. We find a near proportional [C II]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [C II] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [C II] as an H-2 and SFR tracer in such regimes. Finally, based on the observed [C II] and CO radial profiles and different models, we find alpha(CO) to increase with radius, in line with the observed metallicity gradient. The low alpha(CO) (galaxy average less than or similar to 2 M pc(-2) (K km s(-1))(-1)) and low [C II]/CO ratios (similar to 400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.

Massive stars inject mechanical and radiative energy into the surrounding environment, which stirs it up, heats the gas, produces cloud and intercloud phases in the interstellar medium, and disrupts molecular clouds (the birth sites of new stars(1,2)). Stellar winds, supernova explosions and ionization by ultraviolet photons control the lifetimes of molecular clouds(3-7). Theoretical studies predict that momentum injection by radiation should dominate that by stellar winds(8), but this has been difficult to assess observationally. Velocity-resolved large-scale images in the fine-structure line of ionized carbon ([C II]) provide an observational diagnostic for the radiative energy input and the dynamics of the interstellar medium around massive stars. Here we report observations of a one-square-degree region (about 7 parsecs in diameter) of Orion molecular core 1-the region nearest to Earth that exhibits massive-star formation-at a resolution of 16 arcseconds (0.03 parsecs) in the [C II] line at 1.9 terahertz (158 micrometres). The results reveal that the stellar wind originating from the massive star theta(1) Orionis C has swept up the surrounding material to create a 'bubble' roughly four parsecs in diameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per second. This finding demonstrates that the mechanical energy from the stellar wind is converted very efficiently into kinetic energy of the shell and causes more disruption of the Orion molecular core 1 than do photo-ionization and evaporation or future supernova explosions.