Abstract.A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945 has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The study covers the frequency range from 82 GHz to 354 GHz and includes 80 transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are also presented. An analysis of CO and 1.3 mm continuum fluxes indicates that the conversion factor between H 2 column density and CO J = 1−0 integrated intensity is smaller than in the galactic disk by factors of 5−10. A large number of molecular species indicate the presence of a prominent high density interstellar gas component characterized by n H 2 ∼ 10 5 cm −3 . Some spectra show Gaussian profiles. Others exhibit two main velocity components, one at ∼450 km s −1 , the other at ∼710 km s −1 . While the gas in the former component has a higher linewidth, the latter component arises from gas that is more highly excited as is indicated by HCN, HCO + and CN spectra. Abundances of molecular species are calculated and compared with abundances observed toward the starburst galaxies NGC 253 and M 82 and galactic sources. Apparent is an "overabundance" of HNC in the nuclear environment of NGC 4945. While the HNC/HCN J = 1−0 line intensity ratio is ∼0.5, the HNC/HCN abundance ratio is ∼1. From a comparison of K a = 0 and 1 HNCO line intensities, an upper limit to the background radiation of 30 K is derived. While HCN is subthermally excited (T ex ∼ 8 K), CN is even less excited (T ex ∼ 3−4 K), indicating that it arises from a less dense gas component and that its N = 2−1 line can be optically thin even though its N = 1−0 emission is moderately optically thick. Overall, fractional abundances of NGC 4945 suggest that the starburst has reached a stage of evolution that is intermediate between those observed in NGC 253 and M 82. Carbon, nitrogen, oxygen and sulfur isotope ratios are also determined. Within the limits of uncertainty, carbon and oxygen isotope ratios appear to be the same in the nuclear regions of NGC 4945 and NGC 253. S ratios (6.4 ± 0.3, 195 ± 45, 105 ± 25 and 13.5 ± 2.5 in NGC 4945, respectively) appear to be characteristic properties of a starburst environment in which massive stars have had sufficient time to affect the isotopic composition of the surrounding interstellar medium.

With the goal of deriving the physical and chemical conditions of star forming regions in the Large Magellanic Cloud (LMC), a spectral line survey of the prominent star forming region N113 is presented. The observations cover parts of the frequency range from 85 GHz to 357 GHz and include 63 molecular transitions from a total of 16 species, among them spectra of rare isotopologues. Maps of selected molecular lines as well as the 1.2 mm continuum distribution are also presented. Molecular abundances in the core of the complex are consistent with a photon dominated region (PDR) in a nitrogen deficient environment. While CO shows optical depths of order τ ∼10, 13 CO is optically thin. The most prominent lines of CS, HCN, and HCO + show signs of weak saturation (τ ∼0.5). Densities range from 5×10 3 cm −3 for CO to almost 10 6 for CS, HCN, and a few other species, indicating that only the densest regions provide sufficient shielding even for some of the most common species. An ortho-to para-H 2 CO ratio of ∼3 hints at H 2 CO formation in a warm ( > ∼ 40 K) environment. Isotope ratios are 12 C/ 13 C ∼ 49±5, 16 O/ 18 O ∼ 2000±250, 18 O/ 17 O ∼ 1.7±0.2 and 32 S/ 34 S ∼ 15. Agreement with data from other star forming clouds shows that the gas is well mixed in the LMC. The isotope ratios do not only differ from those seen in the Galaxy. They also do not form a continuation of the trends observed with decreasing metallicity 6 Based on observations with the Swedish/ESO Submillimeter Telescope (SEST) at the European Southern Observatory (ESO, La Silla, Chile) and the Atacama Pathfinder EXperiment (APEX, Chajnantor, Chile) of the Max-Planck-Institut für Radioastronomie (MPIfR), ESO, and Onsala Space Observatory (OSO) from the inner to the outer Galaxy. This implies that the outer Galaxy, even though showing an intermediate metallicity, is not providing a transition zone between the inner Galaxy and the metal poor environment of the Magellanic Clouds. A part of this discrepancy is likely caused by differences in the age of the stellar populations in the outer Galaxy and the LMC. While, however, this scenario readily explains measured carbon and oxygen isotope ratios, nitrogen and sulfur still lack a self-consistent interpretation.

Context. The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, high-resolution mid-infrared colour-selected sample of massive young stellar objects (MYSOs). We have identified ∼2000 MYSO candidates located within our Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of our follow-up observations is to identify other objects with similar colours such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. Aims. A critical part of our follow-up programme is to conduct 13 CO molecular line observations in order to determine kinematic distances to all of our MYSO candidates. These distances will be used in combination with far-IR and (sub)millimetre fluxes to determine bolometric luminosities which will allow us to identify and remove nearby low-mass YSOs. In addition these molecular line observations will help in identifying evolved stars which are weak CO emitters. Methods. We have used the 15 m James Clerk Maxwell Telescope (JCMT), the 13.7 m telescope of the Purple Mountain Observatory (PMO), the 20 m Onsala telescope and the 22 m Mopra telescope to conduct molecular line observations towards 508 MYSOs candidates located in the 1st and 2nd Quadrants. These observations have been made at the J = 1−0 (Mopra, Onsala and PMO) and J = 2−1 (JCMT) rotational transition frequency of 13 CO molecules and have a spatial resolution of ∼20 −55 , a sensitivity of T * A 0.1 K and a velocity resolution of ∼0.2 km s −1 . We complement these targeted observations with 13 CO spectra extracted from the Galactic Ring Survey (GRS), which have a velocity resolution of ∼0.21 km s −1 and sensitivity T * A 0.13−0.2 K, towards a further 403 RMS sources. Results. In this paper we present the results and analysis of the 13 CO spectra obtained towards 911 MYSO candidates. We detect 13 CO emission towards 780 RMS sources which corresponds to approximately 84% of those observed. A total of 2595 emission components are detected above 3σ level (typically T * A ≥ 0.3 K), with multiple components being observed towards the majority of these sources -520 sources (∼56%) -with an average of ∼4 molecular clouds detected along each line of sight. These multiple emission features make it difficult to assign a unique kinematic velocity to many of our sample. We have used archival CS (J = 2−1) and maser velocities to resolve the component multiplicity towards 175 sources (∼20%) and have derived a criterion which is used to identify the most likely component for a further 191 multiple component sources. Combined with the single component detections we have obtained unambiguous kinematic velocities for 638 of the 780 MYSOs candidates towards which CO is detected (∼80% of the detections). The 141 sources for which we have not been able to determine the kinematic velocity will require additional line data. Using the rotation curve of Brand and Blitz (1993) and th...

The Serpens filament, as one of the nearest infrared dark clouds, is regarded as a pristine filament at a very early evolutionary stage of star formation. In order to study its molecular content and dynamical state, we mapped this filament in seven species including C 18 O, HCO + , HNC, HCN, N 2 H + , CS, and CH 3 OH. Among them, HCO + , HNC, HCN, and CS show self-absorption, while C 18 O is most sensitive to the filamentary structure. A kinematic analysis demonstrates that this filament forms a velocity-coherent (trans-)sonic structure, a large part of which is one of the most quiescent regions in the Serpens cloud. Widespread C 18 O depletion is found throughout the Serpens filament. Based on the Herschel dust-derived H 2 column density map, the line mass of the filament is 36-41 M ⊙ pc −1 , and its full width at half maximum width is 0.17±0.01 pc, while its length is ≈ 1.6 pc. The inner radial column density profile of this filament can be well fitted with a Plummer profile with an exponent of 2.2±0.1, a scale radius of 0.018 ± 0.003 pc, and a central density of (4.0 ± 0.8) × 10 4 cm −3 . The Serpens filament appears to be slightly supercritical. The widespread blue-skewed HNC and CS line profiles and HCN hyperfine line anomalies across this filament indicate radial infall in parts of the Serpens filament. C 18 O velocity gradients also indicate accretion flows along the filament. The velocity and density structures suggest that such accretion flows are likely due to a longitudinal collapse parallel to the filament's long axis. Both the radial infall rate (∼72 M ⊙ Myr −1 , inferred from HNC and CS blue-skewed profiles) and the longitudinal accretion rate (∼10 M ⊙ Myr −1 , inferred from C 18 O velocity gradients) along the Serpens filament are lower than all previously reported values in other filaments. This indicates that the Serpens filament lies at an early evolutionary stage when collapse has just begun, or that thermal and non-thermal support are effective in providing support against gravity.