Recent H i surveys of the Large Magellanic Cloud (LMC) with the Australia Telescope Compact Array (Kim et al. 1998) and the Parkes multibeam receiver (Staveley-Smith et al. 2003) have focussed, respectively, on the small-scale (< 20 ′ ) structure of the interstellar medium (ISM) and the large-scale (> 1 • ) structure of the galaxy. Using a Fourier-plane technique, we have merged both data sets providing an accurate set of images of the LMC sensitive to structure on scales of 15 pc (for an LMC distance of 50 kpc) upwards. The spatial dynamic range (2.8 orders of magnitude), velocity resolution (1.649 km s −1 ), brightness temperature sensitivity (2.4 K) and column density sensitivity (8.9 × 10 18 cm −2 per 1.649 km s −1 channel) allow for the studies of phenomena ranging from the galaxy-wide interaction of the LMC with its close neighbours to the small-scale injection of energy from supernovae and stellar associations into the ISM of the LMC. This paper presents the merged data and the size spectrum of H i clouds which is similar to the typical size spectrum of the holes and shells in the H i distribution.

We have carried out a survey toward the central regions of 85 starless cores in HCN(J ¼ 1 0) to study inward motions in the cores. Sixty-four cores were detected with HCN lines. The infall asymmetry in the HCN spectra is found to be more prevalent, and more prominent than in any other previously used infall tracers such as CS(J ¼ 2 1), DCO þ (J ¼ 2 1), and N 2 H þ (J ¼ 1 0). We have found a close relation between the intensities of the HCN and N 2 H þ lines. This implies that the HCN is not very depleted in the central regions of the cores. In some cores, the HCN spectra show different signs of asymmetry than other molecular lines. A few cores show various signs of asymmetry in individual HCN hyperfine lines. The distribution of the velocity shift V of the HCN profiles with respect to the systemic velocity of the optically thin tracer is found to be more shifted toward the bluer side than those of other infall tracers, indicating that the HCN traces inward motions more frequently. The V distribution of each HCN hyperfine line for all sources is similar. Moreover, the V values obtained from different HCN hyperfine lines for each source are nearly similar. These may mean that most starless cores are in similar kinematic states across the layers of the cores. We identify 17 infall candidates using all available indicators such as the velocity shift V and the blue-to-red peak intensity ratio of double-peaked profiles for HCN(J ¼ 1 0), CS(J ¼ 2 1), CS(J ¼ 3 2), DCO + (J ¼ 2 1), and N 2 H + (J ¼ 1 0). Four of them, L63, L492, L694-2, and L1197, are found to show a higher blue-to-red ratio in the HCN hyperfine line along the lower opacity, suggesting that infall speed becomes higher toward the center.

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We present large area, fully-sampled maps of the Carina molecular cloud complex in the CO (J = 4 → 3) and neutral carbon [C I] 3 P 1 → 3 P 0 transitions. These data were obtained using the 1.7 meter diameter Antarctic Submillimeter Telescope and Remote Observatory (AST/RO). The maps cover an area of approximately 3 square degrees with a uniform 1 ′ spatial sampling. Analysis of these data, in conjunction with CO (J = 1 → 0) data from the Columbia CO survey and the IRAS HIRES continuum maps for the same region, suggests that the spiral density wave shock associated with the Carina spiral arm may be playing an important role in the formation and dissociation of the cloud complex, as well as in maintaining the internal energy balance of the clouds in this region. Massive stars form at the densest regions of the molecular cloud complex. The winds and outflows associated with these stars have a disrupting effect on the complex and inject mechanical energy into the parent clouds, while the UV radiation from the young stars also heat the parent clouds. The present set of data suggests, however, that massive stars alone may not account for the energetics of the clouds in the Carina region. The details of the data and the correlation among the various data sets hint at the possible role that the spiral density wave shock plays in feeding interstellar turbulence and in heating molecular clouds.

A 21 cm neutral hydrogen interferometric survey of the Large Magellanic Cloud (LMC) combined with the Parkes multi-beam H I single-dish survey clearly shows that the H I gas is distributed in the form of clumps or clouds. The H I clouds and clumps have been identified using a thresholding method with three separate brightness temperature thresholds (T b ). Each catalog of H I cloud candidates shows a power law relationship between the sizes and the velocity dispersions of the clouds roughly following the Larson Law scaling σ v ∝ R 0.5 , with steeper indices associated with dynamically hot regions. The clouds in each catalog have roughly constant virial parameters as a function mass suggesting that the clouds are all in roughly the same dynamical state, but the values of the virial parameter are significantly larger than unity showing that turbulent motions dominate gravity in these clouds. The mass distribution of the clouds is a power law with differential indices between −1.6 and −2.0 for the three catalogs. In contrast, the distribution of mean surface densities is a log-normal distribution.

We present the results of an extensive observational study of the active star-forming complex W51 that was observed in the J = 2 − 1 transition of the 12 CO and 13 CO molecules over a 1.• 25 × 1.• 00 region with the University of Arizona Heinrich Hertz Submillimeter Telescope. We use a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with the distribution of infrared (IR) and radio continuum sources and find associations between molecular clouds and young stellar objects (YSOs) listed in Spitzer IR catalogs. The ratios of CO lines associated with H ii regions are different from the ratios outside the active star-forming regions. We present evidence of star formation triggered by the expansion of the H ii regions and by cloud-cloud collisions. We estimate that about 1% of the cloud mass is currently in YSOs.

We present 737 candidate Young Stellar Objects (YSOs) near the W51 Giant Molecular Cloud (GMC) over an area of 1.25 • × 1.00 • selected from Spitzer Space Telescope data. We use spectral energy distribution (SED) fits to identify YSOs and distinguish them from main-sequence or red giant stars, asymptotic giant branch stars, and background galaxies. Based on extinction of each YSO, we separate a total of 437 YSOs associated with the W51 region from the possible foreground sources. We identify 69 highly embedded Stage 0/I candidate YSOs in our field with masses > 5 M ⊙ (corresponding to mid-to early-B main-sequence spectral types) 46 of which are located in the central active star forming regions of W51A and W51B. From the YSOs associated with W51, we find evidence for mass segregation showing that the most massive YSOs are concentrated on the W51 H II region complex. We find a variation in the spatial distribution of the mass function (MF) of YSOs in the mass range between 5 M ⊙ and 18 M ⊙ . The derived slopes of the MF are −1.26 and −2.36 in the active starforming region and the outer region, respectively. The variation of the MF for YSOs embedded in the molecular cloud implies that the distribution of stellar masses in clusters depends on the local conditions in the parent molecular cloud.

An antenna temperature thresholding algorithm is used on the Bell Laboratories 13 CO Milky Way J p 1 r 0 Survey to create a catalog of 1400 molecular clouds. Of these, 281 clouds are selected for having well-determined kinematic distances. The scale height, luminosity, internal velocity dispersion, and size of the cloud sample are analyzed to show that clouds smaller than ∼ have a scale height which is about 35 pc, roughly independent 5.510 M , of cloud mass, while larger clouds, the giant molecular clouds, have a reduced scale height which declines with increasing cloud mass.