A new survey of the LMC has been completed in 2.6 mm carbon monoxide emission with NANTEN. This survey has revealed 107 giant molecular clouds, the first complete sample of giant molecular clouds in a single galaxy at a linear resolution of ∼ 40 pc. The cloud mass ranges from ∼ 6 × 104 to 2 × 106 M⊙, and the total molecular mass has been estimated to be 4–7 × 107 M⊙ for a molecular column density of ≳ 1.0 × 1021 cm-2, corresponding to 5–10% of the atomic mass. The molecular clouds exhibit a good spatial correlation with the youngest stellar clusters whose ages are ≲ 10 Myr, demonstrating that cluster formation is on-going in these clouds. On the other hand, they show little correlation with older clusters or with supernova remnants, suggesting that the molecular clouds are being rapidly dissipated in a several Myrs, probably due to the UV photons of massive stars in clusters.

Spatial-spatial ('; b) integrated intensity maps for the three transitions observed with ASTRO (top three panels) and, for comparison, the three transitions observed at the BL 7 m (bottom three panels). Transitions are identified at left on each panel. The emission is integrated over all velocities where data are available. These values of (v min , v max ) are: [C i ], (À90, 150); CO(7-6), (À30, 120); CO(4-3), (À150, 150); CO(1-0), (À150, 150); 13 CO(1-0), (À150, 150); CS(2-1), (À150, 150). All six maps have been smoothed to the same 2 0 resolution. The scale on the color bars have been multiplied by 2 to correct for an error in the plotting routine used in the published version of the maps. 395

A key project of the Antarctic Submillimeter Telescope and Remote Observatory reported by Martin et al. (2004) is the mapping of CO J = 4 → 3 and J = 7 → 6 emission from the inner Milky Way, allowing determination of gas density and temperature. Galactic center gas that Binney et al. (1991) identify as being on x 2 orbits has a density near 10 3.5 cm −3 , which renders it only marginally stable against gravitational coagulation into a few Giant Molecular Clouds, as discussed by Elmegreen (1994). This suggests a relaxation oscillator mechanism for starbursts in the Milky Way, where inflowing gas accumulates in a ring at 150 pc radius for approximately 20 million years, until the critical density is reached, and the resulting instability leads to the sudden formation of giant clouds and the deposition of 4 × 10 7 M ⊙ of gas onto the Galactic center.

We have completed a CO ( ) survey for molecular clouds toward the Chamaeleon-Musca Dark Cloud 13J ϭ 1-0 Complex, covering an ∼ area with the NANTEN millimeter-wave telescope. The major result is a ⅙ ⅙ 16 # 17 discovery of 25 small dense clouds widely distributed over ∼ (∼ pc at ∼140 pc), in addition ⅙ ⅙ 11 # 13 28 # 33 to the four previously known large dark clouds. The small clouds show a good spatial correlation with the 33 isolated X-ray-emitting T Tauri stars (TTSs), and most (∼70%) of the 33 TTSs located within 4 pc of the small clouds' boundaries are likely formed in the small clouds. It is argued that the average density, տ10 3 cm , and Ϫ3 mass, ∼20 M , of the small clouds are large enough to form stars in them. The apparent lack of the associated , molecular gas for the remaining TTSs is plausibly explained as a result of cloud dissipation due to the outflow activity of the X-ray TTSs. Based on the present findings, we conclude that the X-ray TTSs were formed in the small dense clouds and that it is not necessary to invoke a runaway TTS hypothesis.

We present fully-sampled maps of 461 GHz CO (4-3), 807 GHz CO (7-6), and 492 GHz [CI] (3P1-3P0) emission from the inner 3 degrees of the Galactic Center region taken with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) in 2001--2002. The data cover -1.3 < l < 2, -0.3 < b < 0.2 with 0.5 arcmin spacing, resulting in spectra in 3 transitions at over 24,000 positions on the sky. The CO (4-3) emission is found to be essentially coextensive with lower-J transitions of CO. The CO (7-6) emission is spatially confined to a far smaller region than the lower-J CO lines. The [CI] (3P1-3P0) emission has a spatial extent similar to the low-J CO emission, but is more diffuse. Bright CO (7-6) emission is detected in the well-known Galactic Center clouds Sgr A and Sgr B. We also detect CO (4-3) and CO (7-6) absorption from spiral arms in the galactic disk at velocities near 0 km s^-1 along the line of sight to the Galactic Center. Analyzing our CO (7-6) and CO (4-3) data in conjunction with J = 1 - 0 12CO and 13CO data previously observed with the Bell Laboratories 7-m antenna, we apply a Large Velocity Gradient (LVG) model to estimate the kinetic temperature and density of molecular gas in the inner 200 pc of the Galactic Center region. We show maps of the derived distribution of gas density and kinetic temperature as a function of position and velocity for the entire region. Kinetic temperature was found to decrease from relatively high values (>70K) at cloud edges to low values (<50K) in the interiors. Typical gas pressures in the Galactic Center gas are n(H_2) T_kin approx 10^5.2 K cm^-3. We also present an (l,b) map of molecular hydrogen column density derived from our LVG results.Comment: 41 pages, 29 figures reduced to low resolution for astro-ph, for high resolution figures please go to http://cfa-www.harvard.edu/ASTRO/galcen_1.pdf this version incorporates changes due to accepted erratum (to appear in ApJS 153