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.

We report Mopra Australia Telescope National Facility (ATNF), Anglo‐Australian Telescope and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large‐scale gravitational infall in the dense gas. From the millimetre and far‐infrared data, the clump has a mass of ∼2 × 104 M⊙, luminosity of ∼2–3 × 104 L⊙ and diameter of ∼0.9 pc. From radiative transfer modelling, we derive a mass infall rate of ∼3.4 × 10−2 M⊙ yr−1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near‐infrared K‐band imaging shows an adjacent compact H ii region and IR cluster surrounded by a shell‐like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual, and we suggest that they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.

Aims. Supernova remnants (SNRs) are believed to be the main sources of Galactic cosmic rays. Molecular clouds associated with SNRs can produce gamma-ray emission by means of the interaction of accelerated particles with the concentrated gas. The middle-aged SNR W28, because of its associated system of dense molecular clouds, provides an excellent opportunity to test this hypothesis. Methods. We present the AGILE/GRID observations of SNR W28, and compare them with observations at other wavelengths (TeV and 12 CO (J = 1 → 0) molecular line emission).Results. The gamma-ray flux detected by AGILE from the dominant source associated with W28 is (14 ± 5) × 10 −8 ph cm −2 s −1 for E > 400 MeV. This source is positionally well correlated with the TeV emission observed by the HESS telescope. The local variations in the GeV to TeV flux ratio imply that there is a difference between the CR spectra of the north-west and south molecular cloud complexes. A model based on a hadronicinduced interaction and diffusion with two molecular clouds at different distances from the W28 shell can explain both the morphological and spectral features observed by both AGILE in the MeV-GeV energy range and the HESS telescope in the TeV energy range. The combined set of AGILE and H.E.S.S. data strongly support a hadronic model for the gamma-ray production in W28.

We have analyzed the atomic and molecular gas using the 21 cm Hi and 2.6/1.3 mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to identify the interstellar medium with which the shock waves of the SNR interact. We have found an Hi intensity depression in the velocity range between −46 and −28 km s −1 toward the SNR, suggesting a cavity in the interstellar medium. The Hi cavity coincides with the thermal and non-thermal emitting X-ray shell. The thermal X-rays are coincident with the edge of the Hi distribution, which indicates a strong density gradient, while the non-thermal X-rays are found toward the less dense, inner part of the Hi cavity. The most significant non-thermal X-rays are seen toward the southwestern part of the shell where the Hi gas traces the dense and cold component. We also identified CO clouds which are likely interacting with the SNR shock waves in the same velocity range as the Hi, although the CO clouds are distributed only in a limited part of the SNR shell. The most massive cloud is located in the southeastern part of the shell, showing detailed correspondence with the thermal X-rays. These CO clouds show an enhanced CO J = 2-1/1-0 intensity ratio, suggesting heating/compression by the shock front. We interpret that the shock-cloud interaction enhances non-thermal X-rays in the southwest and the thermal X-rays are emitted by the shock-heated gas of density 10-100 cm −3 . Moreover, we can clearly see an Hi envelope around the CO cloud, suggesting that the progenitor had a weaker wind than the massive progenitor of the core-collapse SNR RX J1713.7−3949. It seems likely that the progenitor of RCW 86 was a system consisting of a white dwarf and a low-mass star with low-velocity accretion winds.