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.

Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed toward 46 high-mass-star-forming regions. The sample includes UC H ii precursors and UC H ii regions. Seventeen sources are found to show "blue profiles," the expected signature of collapsing cores. The excess of sources with blue over red profiles [ ] is 29% in the HCO ϩ line, with a probability of 0.6% thatthis is caused by random fluctuations. UC H ii regions show a higher excess (58%) than UC H ii precursors (17%), indicating that material is still accreted after the onset of the UC H ii phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low-mass-star-forming regions. Thus, if confirmed for high-mass-star-forming sites, this would point to a fundamental difference between lowand high-mass-star formation. Possible explanations are inadequate thermalization, stronger influence of outflows in massive early cores, larger gas reserves around massive stellar objects, or different trigger mechanisms between low-and high-mass-star formation.

We observed a sample of 35 water masers not coincident with known HII regions and/or low mass young stellar objects (YSOs) with the Effelsberg 100 m telescope in the NH 3 (J, K) = (1, 1), (2, 2), (3, 3) and (4, 4) transitions. Sixteen sources were detected in the NH 3 emission. The detection rate is 46%. All these sixteen sources have NH 3 (1, 1) and (2, 2) emission, among which four sources have NH 3 (3, 3) emission. Comparing with the IRAS and the 2MASS data, we analyzed the relationship between the detection rate and the infrared color, the dust temperature and the source distance. All the detected sources were mapped and 17 cores were obtained (one source IRAS 20215+3725 has two cores). From the detected sources five cores do not coincide with radio continuum or IRAS and MSX point sources. Excluding one core that has no MSX data available, the remaining eleven cores are coincident with IRAS or MSX point sources. The typical size and mass of the cores are 1.6 pc and 1.5 × 10 3 M , respectively. The average line widths of the NH 3 (1, 1) and (2, 2) are 1.54 and 1.73 km s −1 . The average kinetic temperature of the gas is about 19 K. These values are much larger than those of low mass cores. The NH 3 cores that coincide with IRAS sources (referred to as Group I) have slightly larger line widths (1.65 and 1.75 km s −1 for the (1, 1) and (2, 2) lines, respectively) and larger masses (1.8 × 10 3 M ) than the mean values of the sample. For this type of core the kinetic temperature correlates with the line width. The line width appears to correlate with the bolometric luminosity and the core size. Despite the average luminosity of 2.9 × 10 4 L , there is no detectable 6 cm emission. These are candidates for high mass protostars or precursors of UC HII regions. The NH 3 cores with peaks offset from infrared sources (referred to as Group II) have an average size of 1.7 pc and an average line width of 1.50 km s −1 for the (1, 1) line. The line width of the (1, 1) emission is smaller than that of the group I. The average mass is 9.4 × 10 2 M . One possible explanation for the deviation is that the NH 3 peak and the infrared source correspond to different clumps. These cores are potential high mass star formation sites and may be at an earlier evolutionary stage than those with IRAS point sources. This type of core is seen in mapping observations, and can be easily missed by single-spectrum observations toward the IRAS position.

Aims. In an effort to make progress in the current debate on the earliest phases of massive star formation, we took a census of Class 0-like protostellar dense cores in the NGC 3576 region, one of the nearest and most luminous embedded sites of high-mass star formation in the Galaxy. Methods. We used the P-ArTéMiS bolometer camera on the APEX telescope to produce the first 450 μm dust continuum map of the filamentary dense clump associated with NGC 3576. Results. Combining our 450 μm observations with existing data at other wavelengths, we identified seven massive protostellar sources along the NGC 3576 filament and placed them in the M env -L bol evolutionary diagram for protostars. Conclusions. Comparison with theoretical evolutionary tracks suggests that these seven protostellar sources will evolve into massive stars with masses M ∼ 15-50 M . Four sources are classified as candidate high-mass Class 0 objects, two sources as massive Class I objects, and one source appears to be at an intermediate stage.

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.