We present the first results from a new 12CO ($J = 1 \hbox{--} 0$) survey of the Small Magellanic Cloud (SMC) with the NANTEN millimeter-wave telescope. The survey covered the northeast and southwest regions of the main Bar, and the H ii regions N 84, N 88 in the Wing at a linear resolution of $\sim 50 \,\mathrm{pc}$. Twenty-one giant molecular clouds (GMCs), whose masses are $\sim 10^{4} \hbox{--} 10^{6} \,{{{M}_{\odot}}}$, were identified. Significant CO emission, $T_\mathrm{R}^{\ast} \sim 0.36 \,\mathrm{K}$, was first detected toward the N 84 region in the Wing, which is comparable to those of the prominent CO clouds associated with infrared sources LIRS 36, LIRS 49 in the Bar. The GMCs exhibit a good spatial correlation with the H ii regions and young clusters, indicating that cluster formation is on-going in these GMCs. On the other hand, they show little correlation with older clusters or with supernova remnants, suggesting rapid dissipation of CO.

From a 12CO ($J=1 \hbox{--} 0$) survey with the NANTEN telescope, we present a complete catalog of giant molecular clouds (GMCs) in the Large Magellanic Cloud. In total, 107 CO clouds have been identified, 55 of which were detected at more than 3 observed positions. For the 55 clouds, the physical properties, such as size, line-width, virial mass, and CO luminosity, are cataloged. From a statistical analysis of these quantities, we show that GMCs in the LMC are close to gravitational equilibrium. A comparison with H i data indicates that most of the CO clouds are distributed in dense parts of H i gas, whose H i column density is greater than $10^{21} \,\mathrm{cm}^{-2}$. It is notable that the mass ratio of the molecular-to-atomic hydrogen of the lower radial velocity component of gas is $\sim 0.2$, which is a factor of 2 higher than that of the gaseous-disk component, $\sim 0.1$. Molecular clouds are apparently formed efficiently in the parent atomic clouds in the lower velocity component. The CO Arc, which is a few kpc scale ordered structure of CO clouds along the southern optical edge of the galaxy, corresponds well to the the lower velocity component of H i gas.

We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.

We carried out a large-scale survey for molecular clouds in 12CO ($J = 1-0$) emission toward the Chamaeleon region with the NANTEN 4-meter radio telescope at Las Campanas Observatory in Chile. The survey covered $\sim 491 \,\mathrm{deg}^2$ toward $284 {{}^{\circ }} \lesssim l \lesssim 320 {{}^{\circ }}$ and $-34 {{}^{\circ }} \lesssim b \lesssim-6 {{}^{\circ }}$ at an $8^{\prime}$ grid spacing. The total molecular mass in the observed area is estimated to be $\sim 8300 \,{{{M}_{\odot}}}$. More than 60% of the total mass is concentrated in and around the previously known Cha I, II, and III dark clouds. Two cloud complexes having molecular hydrogen masses of $\sim 430 \,{{{M}_{\odot}}}$ and $\sim 1300 \,{{{M}_{\odot}}}$, respectively, have been found at $\sim 10 {{}^{\circ }}$ galactic-east of the Chamaeleon major clouds. We have identified a prominent filament extending from Cha I to the galactic-east direction, which is remarkably long ($\gtrsim 40 \,\mathrm{pc}$) compared with filamentary features found in other dark-cloud complexes. A correlation study between the CO distribution and isolated X-ray emitting T Tauri stars (TTSs) indicates that $\gtrsim 65\%$ of the TTSs are located within 1 pc of the 12CO cloud boundaries. This suggests that low-density parental molecular gas still remains around the isolated TTSs, although the dense parts with density greater than $10^3 \,\mathrm{cm}^{-3}$ have almost dissipated. This provides further support for the local formation of “isolated” T Tauri stars in small clouds.

Based on a new sensitive survey of the giant molecular clouds (GMCs) in the Large Magellanic Cloud, we derived the mass spectrum for them. In the mass range from $\sim8\times10^4\,{{{M}_{\odot}}}$ to $3\times10^6\,{{{M}_{\odot}}}$, a power law with an index value of $-1.9\pm0.1$ shows the best fit to the data. This is consistent with numerical simulations that explain both the H i and CO clumpy distributions by Wada et al. (2000; ApJ, 540, 797), but is significantly steeper than that of the GMCs in the Galaxy. This may be consistent with the drastic dissipation of the GMCs in the LMC due to higher UV radiation fields than in the Galaxy.