Search

Aims. Revealing the 3D dynamics of H-II region bubbles and their associated molecular clouds and H-I envelopes is important for developing an understanding of the longstanding problem as to how stellar feedback affects the density structure and kinematics of the different phases of the interstellar medium. Methods. We employed observations of the H-II region RCW 120 in the [C-II] 158 mu m line, observed within the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program FEEDBACK, and in the (CO)-C-12 and (CO)-C-13 (3 -> 2) lines, obtained with the Atacama Pathfinder Experiment (APEX) to derive the physical properties of the gas in the photodissociation region (PDR) and in the molecular cloud. We used high angular resolution H-I data from the Southern Galactic Plane Survey to quantify the physical properties of the cold atomic gas through H-I self-absorption. The high spectral resolution of the heterodyne observations turns out to be essential in order to analyze the physical conditions, geometry, and overall structure of the sources. Two types of radiative transfer models were used to fit the observed [C-II] and CO spectra. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. To fully exploit the spectral-spatial information in the CO spectra, a Gaussian mixture model was introduced that allows for grouping spectra into clusters with similar properties. Results. The CO emission arises mostly from a limb-brightened, warm molecular ring, or more specifically a torus when extrapolated in 3D. There is a deficit of CO emission along the line-of-sight toward the center of the H-II region which indicates that the H-II region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of i

Context. The interstellar medium is observed to be organized in filamentary structures, and in neutral (H I) and ionized (H II) bubbles. The expanding nature of these bubbles shapes the surrounding medium and possibly plays a role in the formation and evolution of the interstellar filaments. The impact of the expansion of these bubbles on the interstellar medium is not well understood. Aims. Our aim is to describe the kinematics of a filamentary molecular cloud forming high-mass stars and hosting multiple H II regions in order to study the possible environmental impact on the properties of molecular filaments. Methods. We present APEX (CO)-C-13 and (CO)-O-18(2-1) mapping observations of the 10 x 50 pc NGC 6334 molecular cloud complex. We investigated the gas velocity structure along and across the 50 pc long cloud and toward velocity-coherent filaments (VCFs). Results. The NGC 6334 complex is observed to have a coherent velocity structure smoothly varying by similar to 5 km s(-1) over its 50 pc elongation parallel to the Galactic plane. We identify a sample of 75 VCFs in the (CO)-O-18(2-1) position-position-velocity cube and present the properties of 47 VCFs with a length greater than or similar to 1 pc (five beams). We measure a large number of velocity gradients along the VCFs. The amplitudes of these velocity gradients and the velocity dispersion measured along the crests increase with the column density of the VCFs. We derive the column density and velocity power spectra of the VCFs. These power spectra are well represented with power laws showing similar slopes for the two quantities (with a mean of about -2), although some differ by up to a factor of 2. The position velocity diagrams perpendicular to three VCFs (selected from different physical environments) show the V-shaped velocity pattern corresponding to a bent structure in velocity space with the filament at the tip of the V surrounded by an extended structure connected to it with a velocity gradient. Th

Context. Massive stars and their associated ionized (HII) regions could play a key role in the formation and evolution of filaments that host star formation. However, the properties of filaments that interact with HII regions are still poorly known.Aims. To investigate the impact of HII regions on the formation of filaments, we imaged the Galactic HII region RCW 120 and its surroundings where active star formation takes place and where the role of ionization feedback on the star formation process has already been studied.Methods. We used the large-format bolometer camera ArTeMiS on the APEX telescope and combined the high-resolution ArTeMiS data at 350 and 450 mu m with Herschel-SPIRE/HOBYS data at 350 and 500 mu m to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the dense gas distribution around RCW 120 with a resolution of 8 or 0.05 pc at a distance of 1.34 kpc.Results. Our study allows us to trace the median radial intensity profile of the dense shell of RCW 120. This profile is asymmetric, indicating a clear compression from the HII region on the inner part of the shell. The profile is observed to be similarly asymmetric on both lateral sides of the shell, indicating a homogeneous compression over the surface. On the contrary, the profile analysis of a radial filament associated with the shell, but located outside of it, reveals a symmetric profile, suggesting that the compression from the ionized region is limited to the dense shell. The mean intensity profile of the internal part of the shell is well fitted by a Plummer-like profile with a deconvolved Gaussian full width at half maximum of 0.09 pc, as observed for filaments in low-mass star-forming regions.Conclusions. Using ArTeMiS data combined with Herschel-SPIRE data, we found evidence for compression from the inner part of the RCW 120 ionized region on the surrounding dense shell. This compression is accompanied with a significant (factor 5) increase of the local col

Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region. Methods. Our study is based on the Herschel/PACS and SPIRE 70 500 mu m images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract similar to 0.1 pc massive dense cores using the get sources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star. Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.

Context. The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. Many large-scale surveys of the Galactic plane have been conducted recently, allowing for rapid progress in this field. Nevertheless, a sub-arcminute resolution global view of the large-scale distribution of molecular gas, from the diffuse medium to dense clouds and clumps, and of their relationship to the spiral structure, is still missing. Aims. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. Methods. The SEDIGISM survey covers 78 deg(2) of the inner Galaxy (-60 degrees <= l <= 18 degrees, vertical bar b vertical bar <= 0.5 degrees) in the J = 2-1 rotational transition of (CO)-C-13. This isotopologue of CO is less abundant than (CO)-C-12 by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the (CO)-C-13(2-1) and (CO)-O-18(2-1) lines, plus several transitions from other molecules. Results. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. To illustrate the scientific potential of this survey, preliminary results based on a science demonstration field covering -20 degrees <= l <= -18.5 degrees are presented. Analysis of the (CO)-C-13(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary s

Context. The expansion of H II regions can trigger the formation of stars. An overdensity of young stellar objects is observed at the edges of H II regions but the mechanisms that give rise to this phenomenon are not clearly identified. Moreover, it is difficult to establish a causal link between H II -region expansion and the star formation observed at the edges of these regions. A clear age gradient observed in the spatial distribution of young sources in the surrounding might be a strong argument in favor of triggering. Aims. We aim to characterize the star formation observed at the edges of H II regions by studying the properties of young stars that form there. We aim to detect young sources, derive their properties and their evolution stage in order to discuss the possible causal link between the first-generation massive stars that form the H II region and the young sources observed at their edges. Methods. We have observed the Galactic H II region RCW 120 with Herschel PACS and SPIRE photometers at 70, 100, 160, 250, 350 and 500 mu m. We produced temperature and H-2 column density maps and use the getsources algorithm to detect compact sources and measure their fluxes at Herschel wavelengths. We have complemented these fluxes with existing infrared data. Fitting their spectral energy distributions with a modified blackbody model, we derived their envelope dust temperature and envelope mass. We computed their bolometric luminosities and discuss their evolutionary stages. Results. The overall temperatures of the region (without background subtraction) range from 15 K to 24 K. The warmest regions are observed towards the ionized gas. The coldest regions are observed outside the ionized gas and follow the emission of the cold material previously detected at 870 mu m and 1.3 mm. The H-2 column density map reveals the distribution of the cold medium to be organized in filaments and highly structured. Column densities range from 7 x 10(21) cm(-2) up to 9 x 10(23) cm

Aims. To constrain models of high-mass star formation, the Herschel-HOBYS key program aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes. Methods. We used Herschel /PACS and SPIRE 70 500 mu m images of the NGC 6334 complex complemented with (sub) millimeter and mid-infrared data. We built a complete procedure to extract 0.1 pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their spectral energy distributions (SEDs). We also identified the densest pc-scale cloud structures of NGC 6334, one 2 pc x 1 pc ridge and two 0.8 pc x 0.8 pc hubs, with volume-averaged densities of 10(5) cm(-3). Results. A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75 M-circle dot for MDCs in NGC 6334. MDCs have temperatures of 9 : 5 40 K, masses of 75 1000 M-circle dot, and densities of 1 x 10(5) 7 x 10(7) cm(-3). Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70 mu m emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7 x 10(4) yr and at most 3 105 yr respectively, suggest a dynamical scenario of high-mass star formation. Conclusions. The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star

Context. Triggered star formation around H II regions could be an important process. The Galactic H II region RCW79 is a prototypical object for triggered high-mass star formation. Aims. We aim to obtain a census of the young stellar population observed at the edges of the H II region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region. Methods. We take advantage of Herschel data from the surveys HOBYS, Evolution of Interstellar Dust, and Hi-Gal to extract compact sources. We use the algorithm getsources. We complement the Herschel data with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e. g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization-compressed layer of cold and dense gas that is characterized by the column density PDF with a double-peaked lognormal distribution. The 50 sources have sizes of similar to 0.1-0.4 pc with a typical value of similar to 0 : 2 pc, temperatures of similar to 11-26 K, envelope masses of similar to 6 760 M-circle dot, densities of similar to 0.1 44 +/- 10(5) cm(3), and luminosities of similar to 19-12712 L-circle dot. The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass (L-bol-M-env) well. A mass threshold of 140 M fi, determined from the L-bol-M-env diagram, yields 12 candidate massive dense cores that may form high-mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with

Context. The processes leading to the birth of high-mass stars are poorly understood. The key first step to reveal their formation processes is characterising the clumps and cores from which they form. Aims. We define a representative sample of massive clumps in different evolutionary stages selected from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), from which we aim to establish a census of molecular tracers of their evolution. As a first step, we study the shock tracer, SiO, mainly associated with shocks from jets probing accretion processes. In low-mass young stellar objects (YSOs), outflow and jet activity decreases with time during the star formation processes. Recently, a similar scenario was suggested for massive clumps based on SiO observations. Here we analyse observations of the SiO (2-1) and (5-4) lines in a statistically significant sample to constrain the change of SiO abundance and the excitation conditions as a function of evolutionary stage of massive star-forming clumps. Methods. We performed an unbiased spectral line survey covering the 3-mm atmospheric window between 84-117 GHz with the IRAM 30 m telescope of a sample of 430 sources of the ATLASGAL survey, covering various evolutionary stages of massive clumps. A smaller sample of 128 clumps has been observed in the SiO (5-4) transition with the APEX telescope to complement the (2-1) line and probe the excitation conditions of the emitting gas. We derived detection rates to assess the star formation activity of the sample, and we estimated the column density and abundance using both an LTE approximation and non-LTE calculations for a smaller sub-sample, where both transitions have been observed. Results. We characterise the physical properties of the selected sources, which greatly supersedes the largest samples studied so far, and show that they are representative of different evolutionary stages. We report a high detection rate of >75% of the SiO (2-1) line and a >90% detection

Aims. NGC 6334 and NGC 6357 are amongst the most active, optically visible Galactic star-forming complexes. They are composed of several El 11 regions that have a significant impact on their surrounding. The aim of this paper is to present a kinematic study of the optical H II regions that belong to NGC 6334 and NGC 6357. Methods. We use Fabry-Perot interferometer observations of the H alpha line, which cover NGC 6334 and NGC 6357. These observations allow us to analyse the H alpha line profiles to probe the kinematics of the ionised gas of both regions. We complement the H alpha observations with multi-wavelength data to specify the nature of the H II regions. Results. We determine the dynamical nature of the optical H II regions that belongs to NGC 6334 and NGC 6357. In NGC 6334, GUM 61 is an expanding wind shell-like H II region, GUM 64b exhibits a champagne flow, GM1-24 is the H alpha counterpart of two larger regions and H II 351.2+0.5 is, in fact, composed of two H II regions. In NGC 6357, H II 353.08+0.28 and H II 353.09+0.63 are probably stellar wind-shaped bubble 11 II regions, while H II 353.42+0.45 is a classical photo-ionised 11 II region. We suggest that, at large scale, star-formation seems to be triggered where large/old 1111 regions intersect. Inversely, stellar formation seems to have already started in the NGC 6334 north-east filament, irrespective of any evident external H II region impact. While NGC 6357 shows more complicated kinematics, NGC 6334 is characterised by a more active stellar formation.

Aims. We present the first public release of high-quality data products (DR1) from Hi-GAL, the Herschel infrared Galactic Plane Survey. Hi-GAL is the keystone of a suite of continuum Galactic plane surveys from the near-IR to the radio and covers five wavebands at 70, 160, 250, 350 and 500 mu m, encompassing the peak of the spectral energy distribution of cold dust for 8 less than or similar to T less than or similar to 50 K. This first Hi-GAL data release covers the inner Milky Way in the longitude range 68 degrees greater than or similar to l greater than or similar to -70 degrees in a vertical bar b vertical bar <= 1 degrees latitude strip. Methods. Photometric maps have been produced with the ROMAGAL pipeline, which optimally capitalizes on the excellent sensitivity and stability of the bolometer arrays of the Herschel PACS and SPIRE photometric cameras. It delivers images of exquisite quality and dynamical range, absolutely calibrated with Planck and IRAS, and recovers extended emission at all wavelengths and all spatial scales, from the point-spread function to the size of an entire 2 degrees x 2 degrees tile that is the unit observing block of the survey. The compact source catalogues were generated with the CuTEx algorithm, which was specifically developed to optimise source detection and extraction in the extreme conditions of intense and spatially varying background that are found in the Galactic plane in the thermal infrared. Results. Hi-GAL DR1 images are cirrus noise limited and reach the 1 sigma-rms predicted by the Herschel Time Estimators for parallel-mode observations at 60 '' s(-1) scanning speed in relatively low cirrus emission regions. Hi-GAL DR1 images will be accessible through a dedicated web-based image cutout service. The DR1 Compact Source Catalogues are delivered as single-band photometric lists containing, in addition to source position, peak, and integrated flux and source sizes, a variety of parameters useful to assess the quality and

Context. Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of similar to 0.1 pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation. Aims. In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350 mu m. Methods. We used the large-format bolometer camera ArTeMiS on the APEX telescope and combined the high-resolution ArTEMiS data at 350 mu m with Herschel/HOBYS data at 70500 mu m to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8 '' or <0.07 pc at d similar to 1.7 kpc. Results. Our study confirms that this filament is a very dense, massive linear structure with a line mass ranging from similar to 500 M-circle dot/pc to similar to 2000 M-circle dot/pc over nearly 10 pc. It also demonstrates for the first time that its inner width remains as narrow as W similar to 0.15 +/- 0.05 pc all along the filament length, within a factor of <2 of the characteristic 0.1 pc value found with Herschel for lower-mass filaments in the Gould Belt. Conclusions. While it is not completely clear whether the NGC 6334 filament will form massive stars in the future, it is two to three orders of magnitu