We have made CO(J = 2 − 1) observations towards the HII region RCW 49 and its ionizing source, the rich stellar cluster Westerlund 2, with the NANTEN2 sub-mm telescope. These observations have revealed that two molecular clouds in velocity ranges of −11 to +9 km s −1 and 11 to 21 km s −1 respectively, show remarkably good spatial correlations with the Spitzer IRAC mid-infrared image of RCW 49, as well a velocity structures indicative of localized expansion around the bright central regions and stellar cluster. This strongly argues that the two clouds are physically associated with RCW 49. We obtain a new kinematic distance estimate to RCW 49 and Wd2 of 5.4 +1.1 −1.4 kpc, based on the mean velocity and velocity spread of the associated gas. We argue that acceleration of the gas by stellar winds from Westerlund 2 is insufficient to explain the entire observed velocity dispersion of the molecular gas, and suggest a scenario in which a collision between the two clouds ∼4 Myrs ago may have triggered the formation of the stellar cluster. Subject headings: ISM: clouds -open clusters and associations: individual (Westerlund 2) -HII regions: individual (RCW 49)

We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC3603 in the transitions 12 CO(J=2-1, J=1-0) and 13 CO(J=2-1, J=1-0). We suggest that two molecular clouds at 13 km s −1 and 28 km s −1 are associated with NGC3603 as evidenced by higher temperatures toward the H II region as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s −1 . We suggest that the two clouds collided with each other a Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster which is as young as a Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along side Westerlund2 where formation may have been triggered by a cloud-cloud collision. Subject headings: ISM: clouds -open clusters and associations -individual: (NGC3603)the large turbulence excited by the shock interaction. This is the second case of formation of a super star cluster by triggering in a cloud-cloud collision along side Westerlund2 NANTEN2 is an international collaboration of ten universities, Nagoya University,

A large-scale study of the molecular clouds toward the Trifid nebula, M20, has been made in the J=2-1 and J=1-0 transitions of 12 CO and 13 CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures -30-50 K as derived by an LVG analysis -are significantly higher than the 10 K of their surroundings.We identify that the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be ∼ 10 3 M ⊙ and their separation velocity is ∼ 8 km s −1 over ∼1-2 pc. We find the total mass of stars and molecular gas in M20 is less than ∼ 3.2 × 10 3 M ⊙ , which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 s tar, was triggered by the collision between the two clouds in a short time scale of ∼1 Myrs, a second example alongside Westerlund 2, where a super star cluster may have been formed due to cloud-cloud collision triggering. Subject headings: ISM: clouds -Radio lines: ISM -open clusters and associations: individual: M20NANTEN2 is an international collaboration of ten universities, Nagoya University,

Furukawa et al. (2009) reported the existence of a large mass of molecular gas associated with the super star cluster Westerlund 2 and the surrounding HII region RCW49, based on a strong morphological correspondence between NAN-TEN2 12 CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present temperature and density distributions in the associated molecular gas at ∼3.5 pc resolution, as derived from an LVG analysis of the 12 CO(J=2-1), 12 CO(J=1-0) and 13 CO(J=2-1) transitions. The kinetic temperature is as high as ∼60-150 K within a projected distance of ∼5-10 pc from Westerlund 2 and decreases to as low as ∼10 K away from the cluster. The high temperature provides robust verification that the molecular gas is indeed physically associated with the HII region, supporting Furukawa et al.'s conclusion. The derived temperature is also roughly consistent with theoretical calculations of photo dissociation regions (PDRs), while the low spatial resolution of the present study does not warrant a more detailed comparison with PDR models. We suggest that the molecular clouds presented here will serve as an ideal laboratory to test theories on PDRs in future higher resolution studies. Subject headings: ISM: clouds -open clusters and associations: individual (Westerlund 2) -HII regions: individual (RCW 49)

The Census of High-and Medium-mass Protostars (CHaMP) is the first large-scale, unbiased, uniform mapping survey at sub-parsec scale resolution of 90 GHz line emission from massive molecular clumps in the Milky Way. We present the first Mopra (ATNF) maps of the CHaMP survey region (300 • >l>280 • ) in the HCO + J=1→0 line, which is usually thought to trace gas at densities up to 10 11 m −3 . In this paper we introduce the survey and its strategy, describe the observational and data reduction procedures, and give a complete catalogue of moment maps of the HCO + J=1→0 emission from the ensemble of 301 massive molecular clumps. From these maps we also derive the physical parameters of the clumps, using standard molecular spectral-line analysis techniques. This analysis yields the following range of properties: integrated line intensity 1-30 K km s −1 , peak line brightness 1-7 K, linewidth 1-10 km s −1 , integrated line luminosity 0.5-200 K km s −1 pc 2 , FWHM size 0.2-2.5 pc, mean projected axial ratio 2, optical depth 0.08-2, total surface density 30-3000 M ⊙ pc −2 , number density 0.2-30×10 9 m −3 , mass 15-8000 M ⊙ , virial parameter 1-55, and total gas pressure 0.3-700 pPa. We find that the CHaMP clumps do not obey a Larson-type size-linewidth relation. Among the clumps, there exists a large population of subthermally excited, weakly-emitting (but easily detectable) dense molecular clumps, confirming the prediction of Narayanan et al. (2008). These weakly-emitting clumps comprise 95% of all massive clumps by number, and 87% of the molecular mass, in this portion of the Galaxy; their properties are distinct from the brighter massive star-forming regions that are more typically studied. If the clumps evolve by slow contraction, the 95% of fainter clumps may represent a long-lived stage of pressure-confined, gravitationally stable massive clump evolution, while the CHaMP clump population may not engage in vigorous massive star formation until the last 5% of their lifetimes. The brighter sources are smaller, denser, more highly pressurised, and closer to gravitational instability than the less bright sources. Our data suggest that massive clumps approach critical Bonnor-Ebert like states at constant density, while others' suggest that lowermass clumps reach such states at constant pressure. Evidence of global gravitational collapse of massive clumps is rare, suggesting this phase lasts <1% of the clumps' lifetime.