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Aims. In this paper we discuss the physical conditions of clumpy nature in the IC 348 molecular cloud. We show that the millimeter and sub-millimeter line emission from the IC 348 molecular cloud can be modelled as originating from a photon dominated region (PDR).

Context. The fractal structure of the interstellar medium suggests that the interaction of UV radiation with the ISM as described in the context of photon-dominated regions (PDR) dominates most of the physical and chemical conditions, and hence the far-infrared and submm emission from the ISM in the Milky Way.

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.

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 12CO?J = 4 ? 3, J = 7 ? 6, and 13CO?J = 4 ? 3 rotational and [C?I] 3P1-3P0and 3P2-3P1fine-structure transitions. The 13CO?J = 4 ? 3 and [C?i]?3P2-3P1transitions 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 104?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 ?? 220 and an average density of the clump ensemble of about 105?cm-3, thus confirming the presence of high density material in the LMC N159W?region.

Context. Studying molecular gas in the central regions of the star burst galaxies NGC?4945 and Circinus enables us to characterize the physical conditions and compare them to previous local and high-z studies.Aims.We estimate temperature, molecular density and column densities of CO?and atomic carbon. Using model predictions we give a range of estimated CO/C abundance ratios.Methods.Using the new NANTEN2 4?m sub-millimeter telescope in Pampa La Bola, Chile, we observed for the first time CO?4?3 and [Ci]?3P1-3P0at the centers of both galaxies at linear scale of 682?pc and 732?pc respectively. We compute the cooling curves of?12CO and 13CO?using radiative transfer models and estimate the physical conditions of CO?and [CI].Results.The centers of NGC?4945 and Circinus are very [Ci]?bright objects, exhibiting [Ci]?3P1-3P0luminosities of 91 and?67?K?km?s-1?kpc2, respectively. The [Ci]?3P1-3P0/CO?4?3 ratio of integrated intensities are large at 1.2 in NGC?4945 and?2.8 in Circinus. Combining previous CO?J= 1-0, 2?1 and 3?2 and 13CO?J= 1-0, 2?1 studies with our new observations, the radiative transfer calculations give a range of densities, n(H2)=103-3 ?104?cm-3, and a wide range of kinetic temperatures, Tkin= 20-100?K, depending on the density. To discuss the degeneracy in density and temperature, we study two representative solutions. In both galaxies the estimated total [CI] cooling intensity is stronger by factors of ~1-3 compared to the total CO?cooling intensity. The CO/C?abundance ratios are?0.2-2, similar to values found in Galactic translucent clouds. Conclusions.Our new observations enable us to further constrain the excitation conditions and estimate the line emission of higher-J CO- and the upper [CI]-lines. For the first time we give estimates for the CO/C abundance ratio in the center regions of these galaxies. Future CO?J= 7-6 and [CI] 2?1 observations will be important to resolve the ambiguity in the physical conditions and confirm the model predictions.

Aims.We aim at deriving the excitation conditions of the interstellar gas as well as the local FUV intensities in the molecular cloud surrounding NGC 3603 to get a coherent picture of how the gas is energized by the central stars.