No abstract

Abstract. A large scale survey of the Galactic center region in the C18 O(J = 1 → 0) transition is presented. This survey was obtained with the 1.2 m Southern Millimeter-Wave Telescope (SMWT) at the Cerro Tololo Interamerican Observatory (CTIO) near La Serena, Chile. It covers the region −1.• 05 ≤ l ≤ +3.• 6 and −0.• 9 ≤ b ≤ +0.• 75 with a grid spacing of 9 , i.e. the sampling is at full FWHP beamwidth. 357 positions were in total observed. After reviewing the instrumentation of the 1.2 m SMWT, the observing techniques, and the methods used in the data reduction, the data of the survey are presented and morphologically described. In addition, data of the HNCO(5 0,5 − 4 0,4 ) line are presented, which was also included in the large bandwidth of the spectrometer.12 CO(1 − 0) measurements performed for comparison purposes are presented and compared with other 12 CO results. The maps of the C 18 O(1 − 0) survey demonstrate that there are great differences between the distribution of the optically thin C 18 O(1 − 0) emission and the usually optically thick 12 CO(1 − 0) emission.

Abstract. We present the results of a high angular resolution, multi-transition analysis of the molecular gas in M 82. The analysis is based on the two lowest transitions of 12 CO and the ground transition of the rare isotopes 13 CO and C 18 O measured with the PdBI, the BIMA array and the IRAM 30 m telescope. In order to address the question of how the intrinsic molecular cloud properties are influenced by massive star formation we have carried out radiative transfer calculations based on the observed CO line ratios. The calculations suggest that the kinetic temperature of the molecular gas is high in regions with strong star formation and drops towards the outer molecular lobes with less ongoing star formation. The location of the highest kinetic temperature is coincident with that of the mid infrared (MIR) peaks which trace emission from hot dust. The hot gas is associated with low H2 densities while the cold gas in the outer molecular lobes has high H2 densities. We find that CO intensities do not trace H2 column densities well. Most of the molecular gas is distributed in a double-lobed distribution which surrounds the starburst. A detailed analysis of the conversion factor from CO intensity to H2 column density shows that XCO depends on the excitation conditions. We find XCO ∼ T −1 kin n(H2) 1/2 , as expected for virialized clouds.