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Aims. The aim of this work is to study the structure of the protoplanetary disk surrounding the Herbig Ae star HD 163296. Methods. We used high-resolution and high-sensitivity ALMA observations of the CO(3-2) emission line and the continuum at 850 μm, as well as the three-dimensional Monte Carlo radiative transfer code, MCFOST, to model the data presented in this work.Results. The CO(3-2) emission unveils for the first time at submillimeter frequencies the vertical structure details of a gaseous disk in Keplerian rotation, showing the back and front sides of a flared disk. Continuum emission at 850 μm reveals a compact dust disk with a 240 AU outer radius and a surface brightness profile that shows a very steep decline at radius larger than 125 AU. The gaseous disk is more than two times larger than the dust disk, with a similar critical radius but with a shallower radial profile. Radiative transfer models of the continuum data confirm the need for a sharp outer edge to the dust disk. The models for the CO(3-2) channel map require the disk to be slightly more geometrically thick than previous models suggested, and that the temperature at which CO gas becomes depleted (i.e., frozen out) from the outer regions of the disk midplane is T < 20 K, in agreement with previous studies.

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.

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.

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.

Aims. We focus on the kinematical properties of a proto-binary to study the infall and rotation of gas toward its two protostellar components. Methods. We present ALMA Science Verification observations with high-spectral resolution of IRAS 16293-2422 at 220.2 GHz. The wealth of molecular lines in this source and the very high spectral resolution offered by ALMA allow us to study the gas kinematics with unprecedented detail. Results. We present the first detection of an inverse P-Cygni profile toward source B in the three brightest lines. The line profiles are fitted with a simple two-layer model to derive an infall rate of 4.5 × 10 −5 M yr −1 . This infall detection would rule-out the previously suggested possibility that source B is a T Tauri star. A position velocity diagram for source A shows evidence of rotation with an axis close to the line-of-sight.

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.

High-mass star formation is one of the top-priority issues in astrophysics. Recent observational studies are revealing that cloud-cloud collisions may play a role in high-mass star formation in several places in the Milky Way and the Large Magellanic Cloud. The Trifid Nebula M 20 is a well known galactic Hii region ionized by a single O7.5 star. In 2011, based on the CO observations with NANTEN2 we reported that the O star was formed by the collision between two molecular clouds ∼0.3 Myr ago. Those observations identified two molecular clouds towards M 20, traveling at a relative velocity of 7.5 km s −1 . This velocity separation implies that the clouds cannot be gravitationally bound to M20, but since the clouds show signs of heating by the stars there they must be spatially coincident with it. A collision is therefore highly possible. In this paper we present the new CO J=1-0 and J=3-2 observations of the colliding clouds in M 20 performed with the Mopra and ASTE telescopes. The high resolution observations revealed the two molecular clouds have peculiar spatial and velocity structures, i.e., the spatially complementary distribution between the two clouds and the bridge feature which connects the two clouds in velocity space. Based on a new comparison with numerical models, we find that this complementary distribution is an expected outcome of cloud-cloud collisions, and that the bridge feature can be interpreted as the turbulent gas excited at the interface of the collision. Our results reinforce the cloud-cloud collision scenario in M 20.