RX J1713.7−3946 is the most remarkable TeV γ-ray SNR which emits γ-rays in the highest energy range. We made a new combined analysis of CO and H I in the SNR and derived the total protons in the interstellar medium (ISM). We have found that the inclusion of the H I gas provides a significantly better spatial match between the TeV γ-rays and ISM protons than the H 2 gas alone. In particular, the southeastern rim of the γ-ray shell has a counterpart only in the H I. The finding shows that the ISM proton distribution is consistent with the hadronic scenario that comic ray (CR) protons react with ISM protons to produce the γ-rays. This provides another step forward for the hadronic origin of the γ-rays by offering one of the necessary conditions missing in the previous hadronic interpretations. We argue that the highly inhomogeneous distribution of the ISM protons is crucial in the origin of the γ-rays. Most of the neutral gas was likely swept up by the stellar wind of an OB star prior to the SNe to form a low-density cavity and a swept-up dense wall. The cavity explains the low-density site where the diffusive shock acceleration of charged particles takes place with suppressed thermal X-rays, whereas the CR protons can reach the target protons in the wall to produce the γ-rays. The present finding allows us to estimate the total CR proton energy to be ∼10 48 ergs, 0.1 % of the total energy of a SNe.

RCW 120 is a Galactic H II region that has a beautiful ring shape that is bright in the infrared. Our new CO J = 1-0 and J = 3-2 observations performed with the NANTEN2, Mopra, and ASTE telescopes have revealed that two molecular clouds with a velocity separation of 20 km s −1 are both physically associated with RCW 120. The cloud at −8 km s −1 apparently traces the infrared ring, while the other cloud at −28 km s −1 is distributed just outside the opening of the infrared ring, interacting with the H II region as suggested by the high kinetic temperature of the molecular gas and by the complementary distribution with the ionized gas. A spherically expanding shell driven by the H II region is usually considered to be the origin of the observed ring structure in RCW 120. Our observations, however, indicate no evidence of the expanding motion in the velocity space, which is inconsistent with the expanding shell model. We postulate an alternative that, by applying the model introduced by Habe & Ohta, the exciting O star in RCW 120 was formed by a collision between the present two clouds at a collision velocity of ∼30 km s −1 . In the model, the observed infrared ring can be interpreted as the cavity created in the larger cloud by the collision, whose inner surface is illuminated by the strong ultraviolet radiation after the birth of the O star. We discuss that the present cloud-cloud collision scenario explains the observed signatures of RCW 120, i.e., its ring morphology, coexistence of the two clouds and their large velocity separation, and absence of the expanding motion.

Hi-GAL is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 µm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogs presented in Molinari et al. (2016a), covering the portion of Galactic plane −71.0 • < < 67.0 • . The band-merged catalogue contains 100922 sources with a regular SED, 24584 of which show a 70 µm counterpart and are thus considered proto-stellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterise different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in proto-stellar sources compared to prestellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to proto-stellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between "on-arm" and "inter-arm" positions.

Dark gas in the interstellar medium (ISM) is believed to not be detectable either in CO or H i radio emission, but it is detectable by other means including γ rays, dust emission, and extinction traced outside the Galactic plane at |b| > 5• . In these analyses, the 21 cm H i emission is usually assumed to be completely optically thin. We have reanalyzed the H i emission from the whole sky at |b| > 15• by considering temperature stratification in the ISM inferred from the Planck/IRAS analysis of the dust properties. The results indicate that the H i emission is saturated with an optical depth ranging from 0.5 to 3 for 85% of the local H i gas. This optically thick H i is characterized by spin temperature in the range 10 K-60 K, significantly lower than previously postulated in the literature, whereas such low temperature is consistent with emission/absorption measurements of the cool H i toward radio continuum sources. The distribution and the column density of the H i are consistent with those of the dark gas suggested by γ rays, and it is possible that the dark gas in the Galaxy is dominated by optically thick cold H i gas. This result implies that the average density of H i is 2-2.5 times higher than that derived on the optically thin assumption in the local ISM.

We present distributions of two molecular clouds having velocities of 2 and 14 km s −1 toward RCW 38, the youngest super star cluster in the Milky Way, in the 12 CO J = 1-0 and 3-2 and 13 CO J = 1-0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3-2 emission to the J = 1-0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s −1 cloud. We suggest that the collision is currently continuing toward part of the 2 km s −1 cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud-cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.

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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,

A deep survey of the Large Magellanic Cloud at ∼ 0.1−100 TeV photon energies with the Cherenkov Telescope Array is planned. We assess the detection prospects based on a model for the emission of the galaxy, comprising the four known TeV emitters, mock populations of sources, and interstellar emission on galactic scales. We also assess the detectability of 30 Doradus and SN 1987A, and the constraints that can be derived on the nature of dark matter. The survey will allow for fine spectral studies of N 157B, N 132D, LMC P3, and 30 Doradus C, and half a dozen other sources should be revealed, mainly pulsar-powered objects. The remnant from SN 1987A could be detected if it produces cosmic-ray nuclei with a flat power-law spectrum at high energies, or with a steeper index 2.3 − 2.4 pending a flux increase by a factor > 3 − 4 over ∼ 2015 − 2035. Large-scale interstellar emission remains mostly out of reach of the survey if its > 10 GeV spectrum has a soft photon index ∼ 2.7, but degree-scale 0.1 − 10 TeV pion-decay emission could be detected if the cosmic-ray spectrum hardens above >100 GeV. The 30 Doradus star-forming region is detectable if acceleration efficiency is on the order of 1 − 10% of the mechanical luminosity and diffusion is suppressed by two orders of magnitude within < 100 pc. Finally, the survey could probe the canonical velocity-averaged cross section for self-annihilation of weakly interacting massive particles for cuspy Navarro-Frenk-White profiles.