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We present the largest Galactic neutral hydrogen H i absorption survey to date, utilizing the Australian SKA Pathfinder Telescope at an unprecedented spatial resolution of 30 arcsec. This survey, GASKAP-H i , unbiasedly targets 2714 continuum background sources over 250 square degrees in the direction of the Magellanic Clouds, a significant increase compared to a total of 373 sources observed by previous Galactic absorption surveys across the entire Milky Way. We aim to investigate the physical properties of cold (CNM) and warm (WNM) neutral atomic gas in the Milky Way foreground, characterized by two prominent filaments at high Galactic latitudes (between |$-45^{\circ }$| and |$-25^{\circ }$|⁠). We detected strong H i absorption along 462 lines of sight above the 3 |$\sigma$| threshold, achieving an absorption detection rate of 17 per cent. GASKAP-H i 's unprecedented angular resolution allows for simultaneous absorption and emission measurements to sample almost the same gas clouds along a line of sight. A joint Gaussian decomposition is then applied to absorption-emission spectra to provide direct estimates of H i optical depths, temperatures, and column densities for the CNM and WNM components. The thermal properties of CNM components are consistent with those previously observed along a wide range of Solar neighbourhood environments, indicating that cold H i properties are widely prevalent throughout the local interstellar medium. Across our region of interest, CNM accounts for |$\sim$| 30 per cent of the total H i gas, with the CNM fraction increasing with column density towards the two filaments. Our analysis reveals an anticorrelation between CNM temperature and its optical depth, which implies that CNM with lower optical depth leads to a higher temperature. [ABSTRACT FROM AUTHOR]

The Galactic ASKAP survey of OH (GASKAP-OH) is surveying the Milky Way Fourth Quadrant, the Galactic Centre, the Galactic Bulge and the Large Magellanic Cloud (LMC) in the 18-cm ground-state lines of the hydroxyl radical (OH), using Australia's Square Kilometre Array Pathfinder (ASKAP) telescope. With an expected per-channel rms sensitivity of 36 mJy/beam in its shallowest regions, and a velocity channel width of 0.1 km s-1, GASKAP-OH is expected to discover hundreds of new star-formation and evolved star OH masers, as well as extensive absorption from quasi-thermal OH throughout the Galactic Plane. We here summarise the science goals and technical specifications of the survey, and report initial detection results from test observations. GASKAP-OH is expected to run for several years and is an open collaboration. Data products will be made available to the wider community as soon as they are verified. [ABSTRACT FROM AUTHOR]

We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667, and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone, and Galactic Centre over the range | b | < 2°, 332 |$^{\circ }\, \lt l \lt $| 10°, with a small extension between 2 |$^{\circ }\, \lt b \lt $| 6°, 358 |$^{\circ }\, \lt l \lt $| 4°. SPLASH is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of ∼15 mK for an effective velocity resolution of ∼0.9 km s−1. The spectral line datacubes are optimized for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666, and 1720 MHz. Based on initial comparisons with 12CO(J  = 1–0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone. [ABSTRACT FROM AUTHOR]

Using the Australian Square Kilometre Array Pathfinder to measure 21 cm absorption spectra toward continuum background sources, we study the cool phase of the neutral atomic gas in the far outer disk, and in the inner Galaxy near the end of the Galactic bar at longitude 340°. In the inner Galaxy, the cool atomic gas has a smaller scale height than in the solar neighborhood, similar to the molecular gas and the super-thin stellar population in the bar. In the outer Galaxy, the cool atomic gas is mixed with the warm, neutral medium, with the cool fraction staying roughly constant with the Galactic radius. The ratio of the emission brightness temperature to the absorption, i.e., 1 − e−τ, is roughly constant for velocities corresponding to Galactic radius greater than about twice the solar circle radius. The ratio has a value of about 300 K, but this does not correspond to a physical temperature in the gas. If the gas causing the absorption has kinetic temperature of about 100 K, as in the solar neighborhood, then the value 300 K indicates that the fraction of the gas mass in this phase is one-third of the total H i mass. [ABSTRACT FROM AUTHOR]

We investigate the H i envelope of the young, massive GMCs in the star-forming regions N48 and N49, which are located within the high column density H i ridge between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline H i 21 cm line observations with the Australia Telescope Compact Array (ATCA) were combined with archival shorter baseline data and single dish data from the Parkes telescope, for a final synthesized beam size of 24.75 arcsec by 20.48 arcsec, which corresponds to a spatial resolution of ∼6 pc in the LMC. It is newly revealed that the H i gas is highly filamentary and that the molecular clumps are distributed along filamentary H i features. In total 39 filamentary features are identified and their typical width is ∼21 (8–49) [pc]. We propose a scenario in which the GMCs were formed via gravitational instabilities in atomic gas which was initially accumulated by the two shells and then further compressed by their collision. This suggests that GMC formation involves the filamentary nature of the atomic medium. [ABSTRACT FROM AUTHOR]

We have modelled the 3D distribution of OH/IR stars in the Galactic plane, traced by 1612 MHz OH maser sources with classic double horned spectral profiles. We statistically analysed over 700 maser sources detected by the HI/OH/Recombination line survey of the Milky Way (THOR) and the Australia Telescope Compact Array interferometric follow-up observations of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). With a simple model constructed from a classical density distribution of stars and luminosity functions of OH maser sources in the Galaxy, we estimate the scale height, or the half thickness of the OH/IR star distribution along the Galactic disc to be 90–290 pc. The simple model also implies that there are ∼4000 OH/IR stars hosting 1612 MHz OH masers along the Galactic Plane. Therefore, next generation telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP) and SKA Phase 1 will detect about 80 per cent of such OH/IR stars in the Galaxy at a 10 mJy detection limit. Comparing the data of previously detected circumstellar 1612 MHz OH maser sources with those of THOR and SPLASH, the maser source lifetime is estimated to be ∼300 yr. This is likely a lower limit, since non-detections of masers in some cases could be affected by the flux variation of the maser source. [ABSTRACT FROM AUTHOR]

We present new molecular modeling for 14NO and 15NO and a deep, blind molecular line survey at low radio frequencies (99–129 MHz). This survey is the third in a series completed with the Murchison Widefield Array (MWA), but in comparison with the previous surveys, uses 4 times more data (17 hr versus 4 hr) and is 3 times better in angular resolution (1′ versus 3′). The new molecular modeling for nitric oxide and its main isotopologue has seven transitions within the MWA frequency band (although we also present the higher-frequency transitions). Although we did not detect any new molecular lines at a limit of 0.21 Jy beam−1, this work is an important step in understanding the data processing challenges for the future Square Kilometre Array and places solid limits on what is expected in the future of low-frequency surveys. The modeling can be utilized for future searches of nitric oxide. [ABSTRACT FROM AUTHOR]

Observations of the four 2Π3/2,   J  = 3/2 ground state transitions of the hydroxyl radical (OH) have emerged as an informative tracer of molecular gas in the Galactic interstellar medium (ISM). We discuss an OH spectral feature known as the 'flip', in which the satellite lines at 1612 and 1720 MHz flip – one from emission to absorption and the other the reverse – across a closely blended double feature. We highlight 30 examples of the flip from the literature, 27 of which exhibit the same orientation with respect to velocity: the 1720-MHz line is seen in emission at more negative velocities. These same examples are also observed towards bright background continuum, many (perhaps all) show stimulated emission, and 23 of these are coincident in on-sky position and velocity with H  ii  radio recombination lines. To explain these remarkable correlations, we propose that the 1720-MHz stimulated emission originates in heated and compressed post-shock gas expanding away from a central H  ii  region, which collides with cooler and more diffuse gas hosting the 1612-MHz stimulated emission. The foreground gas dominates the spectrum due to the bright central continuum; hence, the expanding post-shock gas is blue-shifted relative to the stationary pre-shock gas. We employ non-local thermodynamic equilibrium (LTE) excitation modelling to examine this scenario and find that indeed FIR emission from warm dust adjacent to the H  ii  region radiatively pumps the 1612-MHz line in the diffuse, cool gas ahead of the expanding shock front, while collisional pumping in the warm, dense shocked gas inverts the 1720-MHz line. [ABSTRACT FROM AUTHOR]

From targeted observations of ground-state hydroxyl (OH) masers towards 702 Methanol Multibeam survey 6.7-GHz methanol masers, in the Galactic longitude range from 186° through the Galactic Centre to 20°, made as part of the 'MAGMO' (Mapping the Galactic Magnetic field through OH masers) project, we present the physical and polarization properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star-forming regions (SFRs). In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of | B LOS| ∼ 6 mG. With limited statistics, we present the in situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers, and water masers, and compare maser positions with mid-infrared images of the parent SFRs. Of the 33 1720-MHz star formation masers, 10 are offset from their central exciting sources, and appear to be associated with outflow activity. [ABSTRACT FROM AUTHOR]

We present observations of the 36-GHz (4−1 → 30  E) and 84-GHz (5−1 → 40  E) class I methanol maser transitions towards a sample of 94 known class I sites. These observations resulted in 93 and 92 detections in the 84- and 36-GHz transitions. While the majority of the 36-GHz sources have been previously reported, many of the sites are observed in the 84-GHz transition for the first time. The near-simultaneous observations of the two transitions revealed strikingly similar spectral profiles and a mean and median 36- to 84-GHz integrated flux density ratio of 2.6 and 1.4. Alongside the 36- and 84-GHz observations, we included rare class II methanol masers at 37.7, 38.3, 38.5, 86.6, and 86.9 GHz, a number of recombination lines, and thermal molecular transitions. We detect one new site of 86.6- and 86.9-GHz methanol masers, as well as six maser candidates in one or more of 37.7-, 38.3-, 38.5-, 86.6-, and 86.9-GHz methanol maser transitions. We detect a relatively higher rate of HC3N compared to that reported by MALT90 (once the respective detection limits were taken into account), who targeted dense dust clumps, suggesting that the class I methanol maser targets incorporate a relatively higher number of warm protostellar sources. We further find that there are similar relationships between the integrated flux density of both class I transitions with the integrated intensity of HC3N, HNC, HCO+, HNC, SiO, and H13CO+. We suggest that this indicates that the integrated flux densities of the 36- and 84-GHz transitions are closely linked to the available gas volume. [ABSTRACT FROM AUTHOR]

H i self-absorption (HISA) clouds are clumps of cold neutral hydrogen (H i) visible in front of warm background gas, which makes them ideal places to study the properties of the cold atomic component of the interstellar medium. The Riegel–Crutcher (R–C) cloud is the most striking HISA feature in the Galaxy. It is one of the closest HISA clouds to us and is located in the direction of the Galactic Centre, which provides a bright background. High-resolution interferometric measurements have revealed the filamentary structure of this cloud; however, it is difficult to accurately determine the temperature and the density of the gas without optical depth measurements. In this paper, we present new H i absorption observations with the Australia Telescope Compact Array against 46 continuum sources behind the R–C cloud to directly measure the optical depth of the cloud. We decompose the complex H i absorption spectra into Gaussian components using an automated machine learning algorithm. We find 300 Gaussian components, from which 67 are associated with the R–C cloud (0 < $v$ LSR < 10 km s−1,  full width at half maximum < 10 km s−1). Combining the new H i absorption data with H i emission data from previous surveys, we calculate the spin temperature and find it to be between 20 and 80 K. Our measurements uncover a temperature gradient across the cloud with spin temperatures decreasing towards positive Galactic latitudes. We also find three new OH absorption lines associated with the cloud, which support the presence of molecular gas. [ABSTRACT FROM AUTHOR]

Emission lines from CO and Hi are the standard tracers of molecular and atomic interstellar medium, respectively. In the past two decades, a consensus has formed that a substantial fraction of Galactic molecular gas evades detection by these two tracers, thus giving rise to the empirical concept of dark molecular gas (DMG). Largely based on the experience and evidence garnered from the Arecibo Millennium survey, we have formed an international consortium, the Pacific Rim Interstellar Matter Observers (PRIMO), to pursue alternative tracers of DMG, particularly absorption against background radio sources (quasars). PRIMO have carried out observing programs at Arecibo, JVLA, Delingha 13.7m, ATCA and ALMA, among others. Our observations reveal abundant hydrides, namely OH and CH, in DMG clouds. The historical difficulty of mapping OH can be explained by the measured OH excitation temperature $f(T_{{\rm{ex}}}^{{\rm{OH}}}) \propto \frac{1}{{\sqrt {2\pi } \sigma }}{\rm{exp}}[ - {(ln(T_{ex}^{OH}) - ln(3.4\;K))^2}/(2{\sigma ^2})],$ which is a modified log-normal function peaking close to the numerical value of the L-band Galactic continuum background (synchrotron + CMB). Both OH and CH are shown to be better tracers of molecular hydrogen than CO, particularly in the intermediate extinction regions (Av ~ 0.05-2 magnitude), where DMG dominates. http://ism.bao.ac.cn/primo [ABSTRACT FROM AUTHOR]

We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, 12CO(J = 1 → 0) and 13CO(J = 1 → 0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl, contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range of 2400–5100 M⊚. The face-on view at a Galactic latitude of b = 0° displays a bar-like structure with an inclination angle of 67.5±2.1° with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low-spatial resolution of the CO and OH maps. [ABSTRACT FROM AUTHOR]

We present results from a study of the dense circumnuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas. We characterize the dense gas traced by HCN, HCO+ and HNC and examine its kinematics in the circumnuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1-0) and HCO+ (1-0) in seven of the nine galaxies and HNC (1-0) in four. Approximately 7 arcsec resolution maps of the circumnuclear molecular gas are presented. The velocity-integrated intensity ratios, HCO+ (1-0)/HCN (1-0) and HNC (1-0)/HCN (1-0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps, we identify photon-dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region. We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray-dominated region chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made. [ABSTRACT FROM AUTHOR]

The statistics of the velocity gradient tensor A=∇u, which embody the fine scales of turbulence, are influenced by turbulent 'structure'. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by A. Structures are studied through the footprints they leave in conditional averages of the Q = -Tr(A²)/2 field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the Q field conditioned upon A and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191-225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the Q field, which is used to validate the stochastic estimation and provide insights towards the model's refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other. [ABSTRACT FROM AUTHOR]

We have made new CO observations of two molecular clouds, which we call “jet” and “arc” clouds, toward the stellar cluster Westerlund 2 and the TeV γ-ray source HESS J1023–575. The jet cloud shows a linear structure from the position of Westerlund 2 on the east. In addition, we have found a new counter jet cloud on the west. The arc cloud shows a crescent shape in the west of HESS J1023–575. A sign of star formation is found at the edge of the jet cloud and gives a constraint on the age of the jet cloud to be ∼Myr. An analysis with the multi CO transitions gives temperature as high as 20 K in a few places of the jet cloud, suggesting that some additional heating may be operating locally. The new TeV γ-ray images by H.E.S.S. correspond to the jet and arc clouds spatially better than the giant molecular clouds associated with Westerlund 2. We suggest that the jet and arc clouds are not physically linked with Westerlund 2 but are located at a greater distance around 7.5 kpc. A microquasar with long-term activity may be able to offer a possible engine to form the jet and arc clouds and to produce the TeV γ-rays, although none of the known microquasars have a Myr age or steady TeV γ-rays. Alternatively, an anisotropic supernova explosion which occurred ∼Myr ago may be able to form the jet and arc clouds, whereas the TeV γ-ray emission requires a microquasar formed after the explosion. [ABSTRACT FROM AUTHOR]

We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions 12CO(J = 2-1, J = 1-0) and 13CO(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 NGC 3603 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 1 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 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision. [ABSTRACT FROM AUTHOR]

An investigation is made into the mechanism of pinch-off for turbulent vortex rings formed by a synthetic jet using time resolved particle image velocimetry measurements in air. During formation, measurements of the material acceleration field show a trailing pressure maximum (TPM) forms behind the vortex core. The adverse pressure gradient behind this TPM inhibits vorticity transport into the ring and the TPM is spatially coincident with the termination of vorticity flux into a control volume moving with the ring. A Lagrangian Coherent Structures (LCS) analysis is shown to be in agreement with the role of the TPM in pinch-off and in identifying the vortex ring before separation. The LCS analysis provides physical insights which form the basis of a revised model of pinch-off, based on kinematics, which predicts the time of formation (formation number) well for the present dataset. The delivery of impulse to the vortex ring is also considered. Two equally important mechanisms are shown to play a role: a material flux and a vortex force. In the case of long maximum stroke ratio, it is demonstrated that a vortex force continues to deliver impulse to the ring after the material flux is terminated at pinch-off and that this contribution may be substantial. This shows that the pinch-off and separation process cannot be considered impulse invariant, which has important implications for unsteady propulsion, present models of vortex ring formation, and existing explanations for vortex ring pinch-off. [ABSTRACT FROM AUTHOR]

We make a comprehensive study of Hi absorption toward H II regions located within ∣l∣ < 10°. Structures in the extreme inner Galaxy are traced using the longitude-velocity space distribution of this absorption. We find significant Hi absorption associated with the Near and Far 3 kpc Arms, the Connecting Arm, Bania's Clump 1, and the Hi Tilted Disk.We also constrain the line-of-sight distances to H II regions, by using Hi absorption spectra together with the H II region velocities measured by radio recombination lines. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope National Facility Mopra 22-m antenna to search for 37.7-GHz (7−2 → 8−1E) methanol masers towards a sample of 36 Class II methanol masers. The target sources are the most luminous Class II methanol masers not previously searched for this transition, with isotropic peak 12.2-GHz maser luminosity greater than 250 Jy kpc2 and isotropic peak 6.7-GHz maser luminosity greater than 800 Jy kpc2. Seven new 37.7-GHz methanol masers were detected as a result of the search. The detection rate for 37.7-GHz methanol masers towards a complete sample of all such Class II methanol maser sites south of declination −20° is at least 30 per cent. The relatively high detection rate for this rare methanol transition is in line with previous predictions that the 37.7-GHz transition is associated with a late stage of the Class II methanol maser phase of high-mass star formation. We find that there is a modest correlation between the ratio of the 6.7- and 37.7-GHz maser peak intensity and the 6.7- and 12.2-GHz maser peak intensity (correlation coefficient 0.63 in a log–log plot). We detected one new 38.3-GHz (62 → 53A−) methanol maser towards G 335.789 + 0.174. This is only the fourth source for which maser emission has been detected in this transition and it is the only one for which emission is not also observed in the 38.5-GHz 62 → 53A+ transition. [ABSTRACT FROM AUTHOR]

In this paper the pressure field during the early development of turbulent vortex rings at two Reynolds numbers is determined using temporally resolved two-dimensional and stereoscopic particle image velocimetry (PIV). The pressure gradient terms are obtained by solving the incompressible Euler equation so that the drag coefficients of the vortex rings can be evaluated. Maxworthy (J. Fluid Mech., vol. 64, 1974, pp. 227–239) and Glezer & Coles (J. Fluid Mech., vol. 211, 1990, pp. 243–283) each developed models to describe the long-term physics of turbulent vortex rings: the former developed a semi-empirical model which permits loss of impulse via the shedding of vorticity into the wake whereas the latter developed a similarity model based on invariance of the hydrodynamic impulse. Maxworthy’s model implies that a significant correction to the similarity solution is required to account for the drag on the vortex ring bubble. We show that during the early development of the turbulent vortex rings the drag is very small and the similarity scaling can basically be retained. [ABSTRACT FROM PUBLISHER]

We present new parsec-scale resolution data from a multiphase study of the ISM in the walls of Galactic supershells. HI synthesis images and CO survey data reveal a wealth of substructure, including dense-tipped fingers and extended molecular clouds embedded in shell walls. We briefly consider formation scenarios for these features, and suggest that both the interaction of an expanding shell with pre-existing dense clouds, as well as in-situ formation of CNM and molecular gas, are likely to be relevant. Future work will also examine the role of instabilities in structure formation and breakup, and will investigate the presence of high-altitude gas associated with supershells and chimneys. [ABSTRACT FROM AUTHOR]

The role of large-scale stellar feedback in the formation of molecular clouds has been investigated observationally by examining the relationship between Hi and 12CO(J = 1−0) in supershells. Detailed parsec-resolution case studies of two Milky Way supershells demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. Recent results on supergiant shells in the LMC suggest that while they do indeed help to organise the ISM into over-dense structures, their global contribution to molecular cloud formation is of the order of only ∼ 10%. [ABSTRACT FROM PUBLISHER]

13CO(J = 2-1) and C18O(J = 2-1) observations of the molecular cloud G285.90+4.53 (Cloud 16) in the Carina Flare supershell (GSH287+04-17) with the APEX telescope are presented. With an algorithm DENDROFIND we identify 51 fragments and compute their sizes and masses. We discuss their mass spectrum and interpret it as being the result of the shell fragmentation process described by the pressure assisted gravitational instability - PAGI. We conclude that the explanation of the clump mass function needs a combination of gravity with pressure external to the shell. [ABSTRACT FROM AUTHOR]