Context. The Cygnus X region is one of the richest star formation sites in the Galaxy. There is a long-standing discussion about whether the region is a chance superposition of several complexes along the line of sight or a single coherent complex at a distance of 1.5 to 2 kpc. Aims. Combining a 13 CO 2 → 1 survey taken with the KOSMA 3 m telescope with mid-IR images from MSX provides a way to improve our understanding of the spatial structure of the complex. The physical properties of the molecular gas can be derived in more detail as it was done in former studies. Methods. Cygnus X has been mapped in 13 CO J = 2 → 1 (10.8 deg 2 ) at an angular resolution of 130 , as well as for smaller areas in 12 CO and 13 CO J = 3 → 2 (90 ), using the KOSMA 3 m submm-telescope. Results. We identified 91 clumps in 13 CO 2 → 1 that have a typical excitation temperature of 10−30 K, an average density of 1.3 × 10 3 cm −3 , radii of 1−8 pc, and masses of a few hundred to several ten thousand M . The main cloud complexes, the northern part (M 2.8 × 10 5 M ) including DR21 and W75N and the southern region (M 4.5 × 10 5 M ) with IC 1318 b/c and AFGL2591, show differences in their physical properties. The 13 CO emission is closely associated with mid-IR emission seen with MSX. We find evidence that Cygnus OB2 and Cygnus OB9 are affecting the molecular material in Cygnus X. Conclusions. Since essentially all molecular cloud complexes in Cygnus X form groups that are connected by molecular emission (visible in channel and position-velocity maps) and partly show evidence of interaction with UV radiation, we conclude that most of the objects seen in this region are located at the same distance, i.e., that of the OB2 cluster at ∼1.7 kpc, which is also consistent with the distances of other OB associations (OB9, OB1) in Cygnus X.

Abstract. We used the KOSMA 3m telescope to map the core 7 × 5 of the Galactic massive star forming region W3 Main in the two fine structure lines of atomic carbon and four mid-J transitions of CO and et al. 1991), this data set allows us to study the physical structure of the molecular cloud interface regions where the occurence of carbon is believed to change from C + to C 0 , and to CO. The molecular gas in W3 Main is warmed by the far ultraviolet (FUV) field created by more than a dozen OB stars. Detailed modelling shows that most of the observed line intensity ratios and absolute intensities are consistent with a clumpy photon dominated region (PDR) of a few hundred unresolved clumps per 0.84 pc beam, filling between 3 and 9% of the volume, with a typical clump radius of 0.025 pc (2.2 ), and typical mass of 0.44 M . The high-excitation lines of CO stem from a 100−200 K layer, as do the [C ] lines. The bulk of the gas mass is however at lower temperatures.

Aims. We present an overview of a high-mass star formation region through the major (sub-)mm, and far-infrared cooling lines to gain insight into the physical conditions and the energy budget of the molecular cloud. Methods. We used the KOSMA 3 m telescope to map the core (10 × 14 ) of the Galactic star-forming region DR21/DR21 (OH) in the Cygnus X region in the two fine structure lines of atomic carbon (C i 3 P 1 − 3 P 0 and 3 P 2 − 3 P 1 ), in four mid-J transitions of CO and 13 CO, and in CS J = 7−6. These observations were combined with FCRAO J = 1−0 observations of 13 CO and C 18 O. Five positions, including DR21, DR21 (OH), and DR21 FIR1, were observed with the ISO/LWS grating spectrometer in the [O i] 63 and 145 µm lines, the [C ii] 158 µm line, and four high-J CO lines. We discuss the intensities and line ratios at these positions and apply the local thermal equilibrium (LTE) and non-LTE analysis methods in order to derive physical parameters such as mass, density and temperature. The CO line emission was modeled up to J = 20.Results. From non-LTE modeling of the low-to high-J CO lines, we identify two gas components, a cold one at temperatures of T kin ∼ 30−40 K and one with T kin ∼ 80−150 K at a local clump density of about n(H 2 ) ∼ 10 4 −10 6 cm −3 . While the cold quiescent component is massive, typically containing more than 94% of the mass, the warm, dense, and turbulent gas is dominated by mid-and high-J CO line emission and its large line widths. The medium must be clumpy with a volume-filling of a few percent. The CO lines are found to be important in cooling the cold molecular gas, e.g. at DR21 (OH). Near the outflow of the UV-heated source DR21, the gas cooling is dominated by line emission of atomic oxygen and of CO. Atomic and ionised carbon play a minor role.

Context. The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only 2.35 kpc distance. Aims. We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas.Methods. The NANTEN2-4 m submillimeter telescope was used to map the [C i] 3 P 1 − 3 P 0 , 3 P 2 − 3 P 1 and CO 4-3, 7-6 lines in two 4 × 4 regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr 14, and the second region is in the molecular cloud south of η Car and Tr 16. These data were combined with 13 CO SEST spectra, HIRES/IRAS 60 µm and 100 µm maps of the FIR continuum, and maps of 8 µm IRAC/Spitzer and MSX emission. Results. We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 10 3 in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8 µm emission lights up at the edges of the molecular clouds, CO and also [C i] appear to trace the H 2 gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38 beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2 × 10 5 cm −3 is needed to reproduce the observed line emission at two selected interface positions. Conclusions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

Context. Star formation at earlier cosmological times took place in an interstellar medium with low metallicity. The Large Magellanic Cloud (LMC) is ideally suited to study star formation in such an environment. Aims. The physical and chemical state of the ISM in a star forming environment can be constrained by observations of submm and FIR spectral lines of the main carbon carrying species, CO, C i and C ii, which originate in the surface layers of molecular clouds illuminated by the UV radiation of the newly formed, young stars. Methods. We present high-angular resolution sub-millimeter observations in the N159W region in the LMC obtained with the NANTEN2 telescope of the 12 CO J = 4 → 3, J = 7 → 6, and 13 CO J = 4 → 3 rotational and [C i]3 P 1 − 3 P 0 and 3 P 2 − 3 P 1 finestructure transitions. The 13 CO J = 4 → 3 and [C i] 3 P 2 − 3 P 1 transitions are detected for the first time in the LMC. We derive the physical and chemical properties of the low-metallicity molecular gas using an escape probability code and a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. Results. The separate excitation analysis of the submm CO lines and the carbon fine structure lines shows that the emitting gas in the N159W region has temperatures of about 80 K and densities of about 10 4 cm −3 . The estimated C to CO abundance ratio close to unity is substantially higher than in dense massive star-forming regions in the Milky Way. The analysis of all observed lines together, including the [C ii] line intensity reported in the literature, in the context of a clumpy cloud PDR model constrains the UV intensity to about χ ≈ 220 and an average density of the clump ensemble of about 10 5 cm −3 , thus confirming the presence of high density material in the LMC N159W region.