In order to study the structure and temperature distribution within high-mass star-forming clumps, we employed the Australia Telescope Compact Array to image the $\mathrm{NH}_3$ (J,K) = (1,1) through (6,6) and the (2,1) inversion transitions, the $\mathrm{H}_2\mathrm{O}$ $6_{16}$-$5_{23}$ maser line at 22.23508 GHz, several $\mathrm{CH}_3\mathrm{OH}$ lines and hydrogen and helium recombination lines. In addition, 22- and 24-GHz radio continuum emission was also imaged.

The $\mathrm{NH}_3$ lines probe the optical depth and gas temperature of compact structures within the clumps. The $\mathrm{H}_2\mathrm{O}$ maser pinpoints the location of shocked gas associated with star formation. The recombination lines and the continuum emission trace the ionised gas associated with hot OB stars. The paper describes the data and presents sample images and spectra towards select clumps. The technique for estimating gas temperature from $\mathrm{NH}_3$ line ratios is described. The data show widespread hyperfine intensity anomalies in the $\mathrm{NH}_3$ (1,1) images, an indicator of non-LTE $\mathrm{NH}_3$ excitation. We also identify several new $\mathrm{NH}_3$ (3,3) masers associated with shocked gas. Towards AGAL328.809+00.632, the $\mathrm{H}_2\mathrm{O}$ $6_{16}$-$5_{23}$ line, normally seen as a maser, is instead seen as a thermally excited absorption feature against a strong background continuum. The data products are described in detail.

Atomic carbon (C0) is one of the most abundant carbon-bearing species in the interstellar molecular gas, and its submillimeter lines are good tracers of low-density molecular clouds which are often dark in CO rotational lines. We present a new map of the central 150 pc region of the Milky Way in the 500 GHz [CI] line, which has been recently obtained with the ASTE 10-m telescope. The [CI] emission is brightest toward the central 5-pc region, where massive GMCs are absent. This [CI]-bright region is approximately centered toward Sgr A*, covering the entire circum-nuclear ring (CND) and the western part of the 50-km/s cloud. The C0/CO abundance ratio is 0.5–2 there, and the highest ratio is observed toward the CND but just outside of the 2-pc ring of dense gas. This discovery may suggest that the CO-dark component occupies a significant fraction of the molecular gas in the circumnuclear region.

Numerical simulations suggest that colliding molecular clouds induce gravitational collapse and may be responsible for star formation. We incorporate magnetic fields in these simulations and present preliminary results of an investigation of the influence of magnetic fields on star formation via this process.

Recent progress is reviewed in describing the physical processes of star cluster formation, from the viewpoint of theoretical models and numerical simulations. In many studies, supersonic turbulent flows structure the gas into a network of clumps, filaments, and cores. Self-gravity drives star formation, moderated by turbulence, magnetic fields, and stellar feedback. Recent models and simulations describe the core mass function, the protostar mass function, and the star-formation rate. Several simulations indicate similar protostar birthrates, a mass advantage for firstborn protostars, and accretion rates that are superthermal and nearly constant. Recently observed core-filament systems with sonic line widths and parsec lengths present challenges for turbulent models.

I review the major science outcomes to date of the Galactic Census of High- and Medium-mass Protostars (CHaMP), and also report the latest observational results on this unbiased, uniform sample of massive, cluster-forming molecular clumps, based on new mm-wave and IR data. These clouds represent the vast, subthermally-excited population of clumps predicted by Narayanan et al. (2008) to dominate the molecular mass of disk galaxies. Besides confirming their existence, we have presented evidence that these massive clumps probably spend a large fraction (90–95%) of their long lives (possibly up to 100 Myr) in a mostly quiescent, low star formation rate (SFR) state. This is likely ended when a density or internal pressure threshold is crossed, after which vigorous, massive cluster formation consumes the densest gas with a high SFR, dispersing the embedding envelope. New results presented in two other posters at this Symposium include (1) the first analysis of HCN emission from the dense gas (Schap et al.2015), and (2) the first deep photometry of clusters in this sample based on NIR AAT & CTIO data, and on MIR Warm Spitzer IRAC data (Dallilar et al.2015).

We present the Three-mm Ultimate Mopra Milky Way Survey, a new mm-wave molecular-line mapping survey of the southern Galactic Plane, and its first data releases and science results. ThrUMMS maps a 60° × 2° sector of our Galaxy's fourth quadrant, using a combination of fast mapping techniques with the Mopra radio telescope, simultaneously in the J = 1→0 lines of 12CO, 13CO, C18O, and CN near 112 GHz, at 1′.2 and 0.3 km s−1 resolution, with 1.2 K/ch sensitivity for 12CO and 0.7 K/ch for the other transitions. The calibrated data cubes from these observations are made freely available to the community on the ThrUMMS website, http://www.astro.ufl.edu/thrumms, after processing through our pipeline. Here, we summarise the first science results, on global variations in the iso-CO line ratios and on a detailed multiwavelength study of the GMCs near l=333°.

The CHaMP project has identified a uniform sample of 303 massive (20–8000 M⊙), dense (200–30,000 cm−3) molecular clumps in a large sector of the southern Milky Way that includes much of the Carina Arm. These are the kinds of clumps that are likely to be the precursors to IRDCs, large stellar clusters, and massive stars. We report new results of the physical conditions in these clouds based on the J=1 → 0 emission at 3mm from the HCN molecule. Analysis of the HCN emission from these clumps reveals that the physical conditions in the gas (i.e., the excitation temperature, optical depth, and column density) do not follow the molecular line emissivity in a straightforward way. This means that large fractions of the molecular material involved in massive cluster formation, while not completely“dark”, are under-luminous and easily missed in certain studies.

Stars are born in turbulent, magnetized filamentary molecular clouds, typically as members of star clusters. Several remarkable technical advances enable observations of magnetic structure and field strengths across many physical scales, from galactic scales on which giant molecular clouds (GMCs) are assembled, down to the surfaces of magnetized accreting young stars. These are shedding new light on the role of magnetic fields in star formation. Magnetic fields affect the gravitational fragmentation and formation of filamentary molecular clouds, the formation and fragmentation of magnetized disks, and finally to the shedding of excess angular momentum in jets and outflows from both the disks and young stars. Magnetic fields play a particularly important role in angular momentum transport on all of these scales. Numerical simulations have provided an important tool for tracking the complex process of the collapse and evolution of protostellar gas since several competing physical processes are at play - turbulence, gravity, MHD, and radiation fields. This paper focuses on the role of magnetic fields in three crucial regimes of star formation: the formation of star clusters emphasizing fragmentation, disk formation and the origin of early jets and outflows, to processes that control the spin evolution of young stars.

We describe an algorithm for constructing fractal molecular clouds that obeys prescribed mass and velocity scaling relations.The algorithm involves a random seed, so that many different realisations corresponding to the same fractal dimension and the same scaling relations can be generated. It first generates all the details of the density field, and then position the SPH particles, so that the same simulation can be repeated with different numbers of particles to explore convergence. It can also be used to initialise finite-difference simulations. We then present preliminary numerical simulations of Hii regions expanding into such clouds, and explore the resulting patterns of star formation. If the cloud has low fractal dimension, it already contains many small self-gravitating condensations, and the principal mechanism of star formation is radiatively driven implosion. This results in star formation occurring quite early, throughout the cloud. The stars resulting from the collapse and fragmentation of a single condensation are often distributed in a filament pointing radially away from the source of ionising radiation; as the remainder of the condensation is dispersed, these stars tend to get left behind in the Hii region. If the cloud has high fractal dimension, the cloud does not initially contain dense condensations, and star formation is therefore delayed until the expanding Hii region has swept up a sufficiently massive shell. The shell then becomes gravitationally unstable and breaks up into protostars. In this collect-and-collapse mode, the protostars are distributed in tangential arcs, they tend to be somewhat more massive, and as the expansion of the shell stalls they move ahead of the ionisation front.

To better characterise infrared dark clouds (IRDCs), and the star formation within them, a comprehensive catalogue of IRDCs has been constructed from the Spitzer GLIMPSE and MIPSGAL archival data. Mosaicing the individual survey blocks together, we have used a new extraction method to identify dark clouds up to 30′ in size, and produce a column density image of each cloud. In total the catalogue contains over 11,000 clouds, defined as connected regions with 8 micron optical depth > 0.35 (corresponding to column densities < 1022 cm−2). The extraction algorithm also identifies sub-structures (fragments) within each cloud. These Spitzer dark clouds (SDCs) range in mass from 10M⊙ to 104M⊙. About 80% of the SDCs were previously unidentified. Only ~ 30% of the SDCs are associated with 24μm point-like sources, leaving the majority of these clouds with no apparent sign of star formation activity. This new catalogue provides an important new resource for future studies of the initial conditions of star formation in the Galaxy.

Multiwavelengths studies of massive star formation regions in the LMC and SMC reveal that a second generation of stars is being formed in dense molecular clouds located in the surroundings of the massive clusters. These dense molecular clouds have survived the action of massive star UV radiation fields and winds and they appear as compact dense H2 knots in regions of weak CO emission. Alternatively, we have found that large molecular clouds, probably remnants of the parental giant molecular clouds where the first generation of stars were formed, are suffering the interaction of the winds and UV radiation field in their surfaces in the direction of the central massive cluster or massive stars. These molecular regions show 1.2 mm continuum emission form cold dust and they show embedded IR sources as determined from deep ground base JHKs imaging. The distribution of young IR sources as determined from their Mid IR colors obtained by SPITZER concentrate in the maxima of CO and dust emission. IR spectroscopy of the embedded sources with high IR excess confirm their nature as massive young stellar objects (MYSO's). Our results are suggestive of contagious star formation where triggering and induced star formation could be taking place.

Two mechanisms of the galactic seed field generation are discussed. One of the mechanisms implies a direct generation of the seed magnetic field through a battery process (Lazarian 1992a). The other accounts for the possibility of the preliminary amplification of the magnetic field on a scale of molecular clouds (Lazarian 1992b). This means that the galactic dynamo can feed on the non-zero average value of the magnetic field amplified by such a small-scale dynamo. It is shown that both mechanisms can generate an adequate seed field. These two scenarios of the seed magnetic field generation can be distinguished by an analysis of the present day galactic magnetic structure.

Magnetic field generation in molecular (atomic) clouds at the early stages of galactic evolution is considered. It is shown that if there is no internal motions immersed the cloud, battery mechanisms (Lazarian 1992a) can account for the generation of thin magnetic shells around clouds insides in plasma with temperature gradients. If turbulent motions are present, the dynamo can be essential. The operation of α — ω, α2 and turbulent dynamos within molecular clouds is discussed. It is shown that the turbulent dynamo leads to generation of magnetic fields in the trace behind the cloud. These magnetic fields within the molecular clouds and in their vicinity are important for the solution of the galactic seed field problem (see Lazarian 1992b) and the formation of structures in clumpy molecular complexes.

We consider the distribution and nature of the gas and star formation in three nearby molecular cloud complexes: Taurus-Auriga, Ophiuchus, and Orion. Large-scale studies show that quite different distributions of dense gas and star formation exist in these regions, but that the global efficiency of star formation, so far, is about 1% in all of these complexes, very similar to the final efficiencies deduced for open clusters and associations. Furthermore, evidence for differences in the initial mass function among these regions is weak; all three regions may be compatible with the initial mass function for open clusters and field stars. Finally, we consider specific examples of star formation in each complex; the results indicate that the ideas of Adams, Lada, and Shu (1987) are reasonably consistent with the data on L1551 IRS 5, in the Taurus cloud, but that modifications are likely to be needed for IRAS 16293-2422 in Ophiuchus and for NGC2071 in Orion.

The properties and structure of six molecular complexes within 500 pc of the Sun are described and compared. They are generally organized into elongated filaments which appear connected to less elongated, more massive clouds. Their prominent star clusters tend to be located in the massive clouds rather than in the filaments. The complexes have similar structure, but big differences in scale, from a few pc to some 30 pc. They show a pattern of regional virial equilibrium, where the massive, centrally located clouds are close to virial equilibrium, while the less massive filaments and other small clouds have too little mass to bind their observed internal motions. Complexes can be ranked according to increasing size, mass, core mass, and the mass and number of the associated stars: they range from Lupus to Taurus to Ophiuchus to Perseus to Orion B to Orion A. The cores in nearby complexes tend to have maps which are elongated, rather than round. The core size, velocity dispersion, and column density of most cores are consistent with virial equilibrium. Cores in Orion tend to exceed cores in Taurus in their line width, size, temperature, mass, and in the mass of the associated star, if any. Stars in Orion tend to be more numerous and more massive than in Taurus, while those in Taurus tend to be more numerous and more massive than in Lupus. The mass of a core tends to increase with the mass of the cloud where it is found, with the mass of the star cluster with which it is associated, and with its proximity to a star cluster. These properties suggest that complexes and their constituent cores and clusters develop together over time, perhaps according to the depth of the gravitational well of the complex.

The small, thin diffuse and translucent molecular clouds are excellent laboratories for studying the ways in which small—scale structure and interstellar chemistry affect each other. Variations of density or column density and chemical stratification can be found on scales as small as 0.01 pc. The origin of such structures and the evolutionary states of small clouds remain elusive.

The current state of our knowledge of the physical parameters and the chemical composition of dense cores in molecular clouds is discussed. In particular, I summarize what is known about the rate at which molecules condense out on grain surfaces. I discuss in turn: a) dense cores in nearby dust complexes such as Taurus, b) clumps in regions of massive star formation such as Orion and M17, c) hot dense cores near to newly formed O stars such as the Orion-KL hot core and d) the high density condensations which give rise to interstellar masers. Recent work on each of these categories is reviewed with emphasis on the chemical abundance determinations and estimates of the local density and temperature. Particular attention is given to recent work on OH, methanol, and ammonia masers.

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104 cm —3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.

IRAS images of nearby molecular clouds show that the mid-IR emission from small particles in the size range 102 to 105 atoms is distributed very differently from the 100 μm emission from large dust grains. Variations in color ratios by as much as one order of magnitude are seen on all angular scales. We summarize observational properties of the color variations and argue that neither their large amplitude nor their morphology can be explained by changes of the excitation by the UV radiation field only. The color variations reflect considerable inhomogeneities in the abundance of small particles. We suggest that the abundance variations are related to the cycling of interstellar matter between the gas phase and dust grains. This interpretation entails that clouds with distinct IR colors differ in their density and velocity structure and that cycling of matter between gas phase and dust grains is more ubiquitous and rapid that generally thought.