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Context. Class I methanol masers are known to be associated with shocked outflow regions around massive protostars, indicating a possible link between the maser properties and those of their host clumps. Aims. The main goals of this study are (1) to search for new class I methanol masers, (2) to statistically study the relationship between class I masers and shock tracers, (3) to compare the properties between class I masers and their host clumps, also as a function of their evolutionary stage and, (4) to constrain the physical conditions that excite multiple class I masers simultaneously. Methods. We analyzed the 3-mm wavelength spectral line survey of 408 ATLASGAL clumps observed with the IRAM 30m-telescope, focusing on the class I methanol masers with frequencies near 84, 95 and 104.3 GHz. Results. We detect narrow, maser-like features towards 54, 100 and 4 sources in the maser lines near 84, 95 and 104.3 GHz, respectively. Among them, fifty 84 GHz masers, twenty nine 95 GHz masers and four rare 104.3 GHz masers are new discoveries. The new detections increase the number of known 104.3 GHz masers from 5 to 9. The 95 GHz class I methanol maser is generally stronger than the 84 GHz maser counterpart. We find 9 sources showing class I methanol masers but no SiO emission, indicating that class I methanol masers might be the only signpost of protostellar outflow activity in extremely embedded objects at the earliest evolutionary stage. Class I methanol masers that are associated with sources that show SiO line wings are more numerous and stronger than those without such wings. The total integrated intensity of class I methanol masers is well correlated with the integrated intensity and velocity coverage of the SiO (2–1) emission. The properties of class I methanol masers are positively correlated with the bolometric luminosity, clump mass, peak H2 column density of their associated clumps but uncorrelated with the luminosity-to-mass ratio, dust temperature, and mean H

Context. Hub-filament systems are suggested to be the birth cradles of high-mass stars and clusters. Aims. We investigate the gas kinematics of hub-filament structures in the G333 giant molecular cloud complex using 13CO (3−2) observed with the APEX/LAsMA heterodyne camera. Methods. We apply the FILFINDER algorithm to the integrated intensity maps of the 13CO J=3−2 line to identify filaments in the G333 complex, and we extract the velocity and intensity along the filament skeleton from moment maps. Clear velocity and density fluctuations are seen along the filaments, allowing us to fit velocity gradients around the intensity peaks. Results. The velocity gradients fitted to the LAsMA data and ALMA data agree with each other over the scales covered by ALMA observations in the ATOMS survey (< 5 pc). Changes of velocity gradient with scale indicate a “funnel” structure of the velocity field in position-position-velocity (PPV) space, indicative of a smooth, continuously increasing velocity gradient from large to small scales, and thus consistent with gravitational acceleration. The typical velocity gradient corresponding to a 1 pc scale is ∼ 1.6 km s−1 pc−1. Assuming free-fall, we estimate a kinematic mass within 1 pc of ∼ 1190 M⊙, which is consistent with typical masses of clumps in the ATLASGAL survey of massive clumps in the inner Galaxy. We find direct evidence for gravitational acceleration from comparison of the observed accelerations to those predicted by free-fall onto dense hubs with masses from millimeter continuum observations. On large scales, we find that the inflow may be driven by the larger scale structure, consistent with hierarchical structure in the molecular cloud and gas inflow from large to small scales. The hub-filament structures at different scales may be organized into a hierarchical system extending up to the largest scales probed, through the coupling of gravitational centers at different scales. Conclusions. We argue that the “funnel” structu

Galactic plane radio surveys play a key role in improving our understanding of a wide range of astrophysical phenomena. Performing such a survey using the latest interferometric telescopes produces large data rates necessitating a shift towards fully or quasi-real-time data analysis with data being stored for only the time required to process them. We present here the overview and set-up for the 3000-h Max-Planck-Institut für Radioastronomie (MPIfR)-MeerKAT Galactic Plane Survey (MMGPS). The survey is unique by operating in a commensal mode, addressing key science objectives of the survey including the discovery of new pulsars and transients and studies of Galactic magnetism, the interstellar medium and star formation rates. We explain the strategy coupled with the necessary hardware and software infrastructure needed for data reduction in the imaging, spectral, and time domains. We have so far discovered 78 new pulsars including 17 confirmed binary systems of which two are potential double neutron star systems. We have also developed an imaging pipeline sensitive to the order of a few tens of micro-Jansky () with a spatial resolution of a few arcseconds. Further science operations with an in-house built S-band receiver operating between 1.7 and 3.5 GHz are about to commence. Early spectral line commissioning observations conducted at S-band, targeting transitions of the key molecular gas tracer CH at 3.3 GHz already illustrate the spectroscopic capabilities of this instrument. These results lay a strong foundation for future surveys with telescopes like the Square Kilometre Array (SKA).

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The Structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium (SEDIGISM) survey has produced high (spatial and spectral) resolution 13CO (2–1) maps of the Milky Way. It has allowed us to investigate the molecular interstellar medium in the inner Galaxy at an unprecedented level of detail and characterise it into molecular clouds. In a previous paper, we have classified the SEDIGISM clouds into four morphologies. However, how the properties of the clouds vary for these four morphologies is not well understood. Here, we use the morphological classification of SEDIGISM clouds to find connections between the cloud morphologies, their integrated properties, and their location on scaling relation diagrams. We observe that ring-like clouds show the most peculiar properties, having, on average, higher masses, sizes, aspect ratios and velocity dispersions compared to other morphologies. We speculate that this is related to the physical mechanisms that regulate their formation and evolution, for example, turbulence from stellar feedback can often results in the creation of bubble-like structures. We also see a trend of morphology with virial parameter whereby ring-like, elongated, clumpy and concentrated clouds have virial parameters in a decreasing order. Our findings provide a foundation for a better understanding of the molecular cloud behaviour based on their measurable properties.

We present one of the very first extensive classifications of a large sample of molecular clouds based on their morphology. This is achieved using a recently published catalogue of 10663 clouds obtained from the first data release of the SEDIGISM survey. The clouds are classified into four different morphologies by visual inspection and using an automated algorithm – J plots. The visual inspection also serves as a test for the J plots algorithm, as this is the first time it has been used on molecular gas. Generally, it has been found that the structure of molecular clouds is highly filamentary and our observations indeed verify that most of our molecular clouds are elongated structures. Based on our visual classification of the 10663 SEDIGISM clouds, 15% are ring-like, 57% are elongated, 15% are concentrated and 10% are clumpy clouds. The remaining clouds do not belong to any of these morphology classes and are termed unclassified. We compare the SEDIGISM molecular clouds with structures identified through other surveys, i.e. ATLASGAL elongated structures and the bubbles from Milky Way Project (MWP). We find that many of the ATLASGAL and MWP structures are velocity coherent. ATLASGAL elongated structures overlap with ≈ 21% of the SEDIGISM elongated structures (elongated and clumpy clouds) and MWP bubbles overlap with ≈ 25% of the SEDIGISM ring-like clouds. We also analyse the starformation associated with different cloud morphologies using two different techniques. The first technique examines star formation efficiency (SFE) and the dense gas fraction (DGF), based on SEDIGISM clouds and ATLASGAL clumps data. The second technique uses the high-mass star formation (HMSF) threshold for molecular clouds. The results indicate that clouds with ring-like and clumpy morphologies show a higher degree of star formation.

The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium) survey that observed a large area of the inner Galaxy in the 13CO (2-1) line at an angular resolution of 28". We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude–velocity map built from the full survey. Additionally, we examine the properties of the molecular clouds in the spiral arms compared to the properties of their counterparts in the inter-arm regions. Through flux and luminosity probability distribution functions, we find that the molecular gas emission associated with the spiral arms does not differ significantly from the emission between the arms. On average, spiral arms show masses per unit length of ⇠ 105 106 M kpc1. This is similar to values inferred from data sets in which emission distributions were segmented into molecular clouds. By examining the cloud distribution across the Galactic plane, we infer that the molecular mass in the spiral arms is a factor of 1.5 higher than that of the inter-arm medium, similar to what is found for other spiral galaxies in the local Universe. We observe that only the distributions of cloud mass surface densities and aspect ratio in the spiral arms show significant differences compared to those of the inter-arm medium; other observed differences appear instead to be driven by a distance bias. By comparing our results with simulations and observations of nearby galaxies, we conclude that the measured quantities would classify the Milky Way as a flocculent spiral galaxy, rather than as a grand-design one.

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Context: The formation processes of massive stars are still unclear but a picture is emerging involving accretion disks and molecular outflows in what appears to be a scaled-up version of low-mass star formation. A census of outflow activity towards high-mass star-forming clumps in various evolutionary stages has the potential to shed light on high-mass star formation. Aims: We conducted an outflow survey towards ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) clumps, using SEDIGISM (structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) data and aimed to obtain a large sample of clumps exhibiting outflow activity in different evolutionary stages. Methods: We identify the high-velocity wings of the 13CO lines, indicating outflow activity, toward ATLASGAL clumps by (1) extracting the simultaneously observed 13CO (2 – 1) and C18O (2 – 1) spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O (core emission) from the 13CO line after considering opacity broadening. Results: We have detected high-velocity gas towards 1192 clumps out of a total sample of 2052 corresponding to an overall detection rate of 58%. Outflow activity has been detected in the earliest (apparently) quiescent clumps (i.e., 70µm weak), to the most evolved H ii region stages i.e., 8µm bright with tracers of massive star formation. The detection rate increases as a function of evolution (quiescent=51%, protostellar=47%, YSO = 57%, UC H ii regions = 76%). Conclusions: Our sample is the largest outflow sample identified so far. The high-detection rate from this large sample is consistent with the results of similar studies reported in the literature and supports the scenario that outflows are a ubiquitous feature of highmass star formation. The lower detection rate in early evolutionary stages may be due to the fact that outflows in the early stages are weak and difficult to detect. We obtain a statistically significant sample of outflow clumps for e

Context. Understanding the effect of feedback from young massive stars on the star-forming ability of their parental molecular clouds is of central importance for studies of the interstellar medium and star formation. Aims. We observed the G305 star-forming complex in the J = 3-2 lines of 12CO and 13CO to investigate whether feedback from the central OB stars was triggering star formation in G305 or actually disrupting this process. Methods. The region was decomposed into clumps using dendrogram analysis. A catalog of the clump properties such as their positions, luminosities, masses, radii, velocity ispersions, volume densities, and surface mass densities was created. The surface mass densities of the clumps were plotted as a function of the incident 8 µm flux. A mask of the region with 8 µm flux > 100 MJy/sr was created and clumps were categorized into three classes based on their extent of overlap with the mask, namely mostly inside (>67% overlap), partly inside (>10% and <67% overlap), and outside (<10% overlap). The surface mass density distribution of each of these populations was separately plotted. This was followed by comparing the G305 clumps with the Galactic average taken from a distance-limited sample of ATLASGAL and CHIMPS clumps. Finally, the cumulative distribution functions (CDFs) of the clump masses in G305 and their L/M ratios were compared to that of the Galactic sample to determine which mechanism of feedback was dominant in G305. Results. The surface mass densities of clumps showed a positive correlation with the incident 8 µm flux. The data did not have sufficient velocity resolution to discern the effects of feedback on the linewidths of the clumps. The subsample of clumps labeled mostly inside had the highest median surface mass densities followed by the partly inside and outside subsamples. The difference between the surface mass density distribution of the three subsamples were shown to be statistically significant using the Kolmogorov–Smi

Context. Understanding the effect of feedback, the interaction of young massive stars with their parental Giant Molecular Clouds, is of central importance for studies of the interstellar medium and star formation. Aims. We observed the G305 star forming complex in the J = 3-2 lines of \(^{12}\)CO and \(^{13}\)CO to investigate how molecular gas surrounding the central stellar clusters is being impacted by feedback. Methods. The APEX telescope’s LAsMA multi-beam receiver was used to observe the region. Excitation temperatures and column density maps were produced. Combining our data with data from the SEDIGISM survey resulted in a \(^{13}\)CO J = 3-2/2-1 excitation map. To verify whether feedback from stellar clusters is responsible for exciting the gas, the distribution of CO excitation was compared with that of 8 µm emission imaged with Spitzer, which is dominated by UV-excited emission from PAHs. Line centroid velocities, as well as stacked line profiles were examined to investigate the effect of feedback on the gas dynamics. Results. Line profiles along radially outward directions demonstrate that the excitation temperature and \(^{13}\)CO J = 3-2/2-1 ratio increase steeply by factors of ∼ 2–3 at the edge of the denser gas traced by \(^{13}\)CO that faces the hot stars at the center of the complex and steadily decreases away from it. Column density also increases at the leading edge, but does not always decrease steadily outward. Regions with higher 8 µm flux have higher median excitation temperatures, column densities and \(^{13}\)CO J = 3-2/2-1 ratio. The centroid velocity probability distribution function of the region shows exponential wings, indicative of turbulence driven by strong stellar winds. Stacked spectra in regions with stronger feedback have higher skewness and narrower peaks with pronounced wings compared to regions with weaker feedback. Conclusions. Feedback from the stellar cluster in G305 has demonstrable effects on the excitation as well as on

Context. Star-formation in the outer Galaxy is thought to be different from the inner Galaxy, as it is subject to different environmental parameters such as metallicity, interstellar radiation field, or mass surface density that all change with Galactocentric radius. Extending our knowledge on star-formation from the inner to the outer Galaxy helps us to understand the influences of the change of the environment on star formation throughout the Milky Way. Aims. We therefore aimed at getting a more detailed view on the structure of the outer Galaxy, determining physical properties for a large number of star forming clumps and understanding star-formation outside the Solar circle. As one of the largest expanding Galactic supershells is present in the observed region, a unique opportunity is used here to investigate the influence of such an expanding structure on star-formation as well. Methods. We use pointed \(^{12}\)CO(2–1) observations conducted with the APEX telescope to determine the velocity components towards 830 dust clumps identified from 250 µm Herschel/Hi-GAL SPIRE emission maps in the outer Galaxy between 225° < \(\ell\) < 260°. We determined kinematic distances from the velocity components, in order to analyze the structure of the outer Galaxy and to estimate physical properties such as dust temperatures, bolometric luminosities, clump masses, and H\(_2\) column densities for 611 clumps. For this, we determined the dust spectral energy density distributions from archival mid-infrared to sub-millimeter emission maps. Results. We find the identified CO clouds to be strongly correlated with the highest column density parts of the Hi emission distribution, spanning a web of bridges, spurs and blobs of star forming regions between the larger complexes, unveiling the complex three-dimensional structure of the outer Galaxy in unprecedented detail. Using the physical properties of the clumps, we find an upper limit of 6% (40 sources) to be able to form high-mass

Aims. We study ten molecular transitions obtained from an unbiased 3 mm molecular line survey using the IRAM 30 m telescope toward 409 compact dust clumps identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) to understand photodissociation regions (PDRs) associated with the clumps. The main goal of this study is to investigate whether the abundances of the selected molecules show any variations resulting from the PDR chemistry in different clump environments. Methods. We selected HCO, HOC\(^+\), C\(_2\)H, c-C\(_3\)H\(_2\), CN, H\(^{13}\)CN, HC\(^{15}\)N, and HN\(^{13}\)C as PDR tracers, and H\(^{13}\)CO\(^+\) and C\(^{18}\)O as dense gas tracers. By using estimated optical depths of C\(_2\)H and H\(^{13}\)CN and assuming optically thin emission for other molecular transitions, we derived column densities of those molecules and their abundances. To assess the influence of the presence and strength of ultraviolet radiation, we compare abundances of three groups of the clumps: Hii regions, infrared bright non-Hii regions, and infrared dark non-Hii regions. Results. We detected C\(^{18}\)O, H\(^{13}\)CO\(^+\), C\(_2\)H, c-C\(_3\)H\(_2\), CN and HN\(^{13}\)C toward most of the observed dust clumps (detection rate > 94%), and H\(^{13}\)CN is also detected with a detection rate of 75%. On the other hand, HCO and HC\(^{15}\)N show detection rates of 32% and 39%, respectively, toward the clumps, which are mostly associated with Hii region sources: detection rates of HCO and HC\(^{15}\)N toward the Hii regions are 66% and 79%. We find that the abundances of HCO, CN, C\(_2\)H, and c-C\(_3\)H\(_2\) decrease as the H\(_2\) column density increase, indicating high visual extinction, while those of high density tracers (i.e., H\(^{13}\)CO\(^+\) and HC\(^{15}\)N) are constant. In addition, N(HCO)/N(H\(^{13}\)CO\(^+\)) ratios significantly decrease as H\(_2\) column density increase, and in particular, 82 clumps have X(HCO) \(\gtrapprox\) 10\(^{−10}\) and N(HC

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (\(DGF_{gmc} = ∑M_{clump}/M_{gmc}\)) and the instantaneous star forming efficiencies (i.e., \(SFE_{gmc} = ∑L_{clump}/M_{gmc}\)). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms (∼60 per cent found within ±10 km s\(^{−1}\) of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and HI to H\(_2\) conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process.

Molecular clouds form from the atomic phase of the interstellar medium. However, characterizing the transition between the atomic and the molecular interstellar medium (ISM) is a difficult observational task. Here we address cloud formation processes by combining H I self absorption (HISA) with molecular line data. Column density probability density functions (N-PDFs) are a common tool to examine molecular clouds. One scenario proposed by numerical simulations is that the N-PDF evolves from a log-normal shape at early times to a power-law-like shape at later times. To date, investigations of N-PDFs are mostly limited to the molecular component of the cloud. In this paper, we study the cold atomic component of the giant molecular filament GMF38.1-32.4a (GMF38a, distance=3.4 kpc, length∼ 230 pc), calculate its N-PDFs and study its kinematics. We identify an extended HISA feature, which is partly correlated with the \(^{13}\)CO emission. The peak velocities of the HISA and \(^{13}\)CO observations agree well on the eastern side of the filament, whereas a velocity offset of approximately 4 km s\(^{−1}\) is found on the western side. The sonic Mach number we derive from the linewidth measurements shows that a large fraction of the HISA, which is ascribed to the cold neutral medium (CNM), is at subsonic and transonic velocities. The column density of the CNM part is on the order of 10\(^{20}\) to 10\(^{21}\) cm\(^{−2}\). The column density of molecular hydrogen, traced by \(^{13}\)CO, is an order of magnitude higher. The N-PDFs from HISA (CNM), H I emission (the warm and cold neutral medium), and \(^{13}\)CO (molecular component) are well described by log-normal functions, which is in agreement with turbulent motions being the main driver of cloud dynamics. The N-PDF of the molecular component also shows a power law in the high column-density region, indicating self-gravity. We suggest that we are witnessing two different evolutionary stages within the filament. The easte

Aims: In order to understand the observed molecular diversity in high-mass star-forming regions, one has to discern the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods: We present a detailed observational and modeling study of the hot core VLA3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37mm with an angular resolution of ~0.0042 (1 400 au at 3.33 kpc), we derived the physical and chemical structure of the source. We modeled the observed molecular abundances with the chemical evolution code MUSCLE (MUlti Stage ChemicaL codE. Results: With the kinetic temperature tracers CH3CN and H2CO we observe a temperature distribution with a power-law index of q = 0:41+- 0:08. Using the visibilities of the continuum emission we derive a density structure with a power-law index of p = 1:7 +- 0:1. The hot core spectra reveal high molecular abundances and a rich diversity in complex molecules. The majority of the molecules have an asymmetric spatial distribution around the forming protostar(s), which indicates a complex physical structure on scales < 1 400 au. Using MUSCLE, we are able to explain the observed molecular abundance of 10 out of 14 modeled species at an estimated hot core chemical age of ~21 100 years. In contrast to the observational analysis, our chemical modeling predicts a lower density power-law index of p < 1:4. Reasons for this discrepancy are discussed. Conclusions: Combining high spatial resolution observations with detailed chemical modeling allows us to derive a concise picture of the physical and chemical structure of the famous AFGL 2591 hot core. The next steps are to conduct similar analysis for the whole CORE sample and by that constrain the chemical diversity in high-mass star formation to much greater depth.

Context: High-mass stars are formed within massive molecular clumps, where a large number of stars form close together. The evolution of the clumps with different masses and luminosities is mainly regulated by its high-mass stellar content and the formation of such objects is still not well understood. Aims. In this work, we characterise the mid-J CO emission in a statistical sample of 99 clumps (TOP100) selected from the ATLASGAL survey that are representative of the Galactic proto-cluster population. Methods: High-spatial resolution APEX-CHAMP+ maps of the CO (6–5) and CO (7–6) transitions were obtained and combined with additional single-pointing APEX-FLASH+ spectra of the CO (4–3) line. The data were convolved to a common angular resolution of 13??.4. We analysed the line profiles by fitting the spectra with up to three Gaussian components, classified as narrow or broad, and computed CO line luminosities for each transition. Additionally, we defined a distance-limited sample of 72 sources within 5 kpc to check the robustness of our analysis against beam dilution effects. We study the correlations of the line luminosities and profiles for the three CO transitions with the clump properties and investigate if and how they change as a function of the evolution. Results: All sources were detected above 3-? in all three CO transitions and most of the sources exhibit broad CO emission likely associated with molecular outflows. We found that the extension of the mid-J CO emission is correlated with the size of the dust emission traced by the Herschel-PACS 70 µm maps. The CO line luminosity (LCO) is correlated with the luminosity and mass of the clumps. However, it does not correlate with the luminosity-to-mass ratio. Conclusions: The dependency of the CO luminosity with the properties of the clumps is steeper for higher-J transitions. Our data seem to exclude that this trend is biased by self-absorption features in the CO emission, but rather suggest that different J tr

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Analysing the kinematics of filamentary molecular clouds is a crucial step towards understanding their role in the star formation process. Therefore, we study the kinematics of 283 filament candidates in the inner Galaxy, that were previously identified in the ATLASGAL dust continuum data. The 13CO(2 – 1) and C18O(2 – 1) data of the SEDIGISM survey (Structure, Excitation, and Dynamics of the Inner Galactic Inter Stellar Medium) allows us to analyse the kinematics of these targets and to determine their physical properties at a resolution of 30'' and 0.25 km s?1 . To do so, we developed an automated algorithm to identify all velocity components along the line-of-sight correlated with the ATLASGAL dust emission, and derive size, mass, and kinematic properties for all velocity components. We find two-third of the filament candidates are coherent structures in position-position-velocity space. The remaining candidates appear to be the result of a superposition of two or three filamentary structures along the line-of-sight. At the resolution of the data, on average the filaments are in agreement with Plummer-like radial density profiles with a power-law exponent of p ? 1.5 ± 0.5, indicating that they are typically embedded in a molecular cloud and do not have a well-defined outer radius. Also, we find a correlation between the observed mass per unit length and the velocity dispersion of the filament of m ? ?V^2. We show that this relation can be explained by a virial balance between self-gravity and pressure. Another possible explanation could be radial collapse of the filament, where we can exclude infall motions close to the free-fall velocity.

Context: The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. Aims: We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. Methods: This OH study is part of the Hi/OH/Recombination line survey of the inner Milky Way (THOR). THOR is a Karl G. Jansky Very Large Array (VLA) large program of atomic, molecular and ionized gas in the range 15? ? l ? 67? and |b| ? 1?. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the optical depths derived from these observations with literature 13CO(1-0) and Hi observations to determine the OH abundance. Results. We detect absorption in the 1665 and 1667MHz transitions, that is, the “main” hyperfine structure lines, for continuum sources stronger than Fcont ? 0.1 Jy beam?1. OH absorption is found against approximately 15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption occurs in molecular clouds that are associated with Galactic Hii regions. We find OH and 13CO gas to have similar kinematic properties. The data indicate that the OH abundance decreases with increasing hydrogen column density. The derived OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for AV < 10 ? 20. Towards the lowest column densities, we find sources that exhibit OH absorption but no 13CO emission, indicating that OH is a well suited tracer of the low column density molecular gas. We also present spatially resolved OH absorption towards the prominent extended Hii-region W43. Conclusions: The unbiased nature of the THOR survey opens a new window onto the gas properties of the interstellar medium. The characterization of the OH abundance over a large range

The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised. Using the IRAM NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum emission. We present the spectral line setup of the CORE survey and a case study for W3(H2O). At ~0.35" (700 AU at 2 kpc) resolution, the W3(H2O) clump fragments into two cores (West and East), separated by ~2300 AU. Velocity shifts of a few km/s are observed in the dense-gas tracer, CH3CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from each core. The kinematics of the rotating structure about W3(H2O) W shows signs of differential rotation of material, possibly in a disk-like object. The observed rotational signature around W3(H2O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combination of both. We fit the emission of CH3CN (12-11) K = 4-6 and derive a gas temperature map with a median temperature of ~165 K across W3(H2O). We create a Toomre Q map to study the stability of the rotating structures against gravitational instability. The rotating structures appear to be Toomre unstable close to their outer boundaries, with a possibility of further fragmentation in the differentially-rotating core W3(H2O) W. Rapid cooling in the Toomre-unstable regions supports the fragmentation scenario. Combining millimeter dust continuum and spectral line data toward the famous high-mass star-forming region W3(H2O), we identify core fragmentation on large scales, and indications for possible disk fragmentation on smaller spatial scales.

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ATLASGAL is an unbiased 870 micron submillimetre survey of the inner Galactic plane. It provides a large and systematic inventory of all massive, dense clumps in the Galaxy (>1000 Msun) and includes representative samples of all embedded stages of high-mass star formation. Here we present the first detailed census of the properties (velocities, distances, luminosities and masses) and spatial distribution of a complete sample of ~8000 dense clumps located in the Galactic disk. We derive highly reliable velocities and distances to ~97% of the sample and use mid- and far-infrared survey data to develop an evolutionary classification scheme that we apply to the whole sample. Comparing the evolutionary subsamples reveals trends for increasing dust temperatures, luminosities and line-widths as a function of evolution indicating that the feedback from the embedded proto-clusters is having a significant impact on the structure and dynamics of their natal clumps. We find 88\,per\,cent are already associated with star formation at some level. We also find the clump mass to be independent of evolution suggesting that the clumps form with the majority of their mass in-situ. We estimate the statistical lifetime of the quiescent stage to be ~5 x 10^4 yr for clump masses ~1000 Msun decreasing to ~1 x 10^4 yr for clump masses >10000 Msun. We find a strong correlation between the fraction of clumps associated with massive stars and peak column density. The fraction is initially small at low column densities but reaching 100\,per\,cent for column densities above 10^{23} cm^{-2}; there are no clumps with column density clumps above this value that are not already associated with massive star formation. All of the evidence is consistent with a dynamic view of star formation wherein the clumps form rapidly and are initially very unstable so that star formation quickly ensues.

Context: There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. This deficiency is thought to be caused by a lack of sensitive radio continuum data. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of H ii regions makes identifying such features challenging. SNRs can, however, be separated from H ii regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. Aims: Our goal is to find missing SNR candidates in the Galactic disk by locating extended radio continuum sources that lack MIR counterparts. Methods: We use the combination of high-resolution 1–2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with H ii regions, we exclude radio continuum sources from the WISE Catalog of Galactic H ii Regions, which contains all known and candidate H ii regions in the Galaxy. Results: We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4° > ℓ > 17.5°, | b | ≤ 1.25° and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near ℓ ≃ 30°, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4′ ± 4.7′ versus 11.0′ ± 7.8′, and have lower integrated flux densities. Conclusions: The THOR survey shows that sensitive radio continuum data can discover a large number of SNR candidates, and that these candidates can be efficiently identified using the combination of radio and MIR data. If th