Search

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. [ABSTRACT FROM AUTHOR]

Context. High-mass analogues of low-mass prestellar cores are searched for to constrain the models of high-mass star formation. Several high-mass cores, at various evolutionary stages, have been recently identified towards the massive star-forming region W43-MM1 and amongst them a high-mass prestellar core candidate. Aims. We aim to characterise the chemistry in this high-mass prestellar core candidate, referred to as W43-MM1 core #6, and its environment. Methods. Using ALMA high-spatial resolution data of W43-MM1, we have studied the molecular content of core #6 and a neighbouring high-mass protostellar core, referred to as #3, which is similar in size and mass to core #6. We first subtracted the continuum emission using a method based on the density distribution of the intensities on each pixel. Then, from the distribution of detected molecules, we identified the molecules centred on the prestellar core candidate (core #6) and those associated to shocks related to outflows and filament formation. Then we constrained the column densities and temperatures of the molecules detected towards the two cores. Results. While core #3 appears to contain a hot core with a temperature of about 190 K, core #6 seems to have a lower temperature in the range from 20 to 90 K from a rotational diagram analysis. We have considered different source sizes for core #6 and the comparison of the abundances of the detected molecules towards the core with various interstellar sources shows that it is compatible with a core of size 1000 au with T = 20−90 K or a core of size 500 au with T ~ 80 K. Conclusions. Core #6 of W43-MM1 remains one of the best high-mass prestellar core candidates even if we cannot exclude that it is at the very beginning of the protostellar phase of high-mass star formation. [ABSTRACT FROM AUTHOR]

Context. The physical conditions during high-mass star formation are poorly understood. Outflow and infall motions have been detected around massive protostellar objects, but their dependence on mass, luminosity, and age is unclear. In addition, physical conditions and molecular abundances are often estimated using simple assumptions such as spherical shape and chemical homogeneity, which may limit the accuracy of the results. Aims. We aim to characterize the dust and gas distribution and kinematics of the envelopes of high-mass protostars. In particular, we search for infall motions, abundance variations, and deviations from spherical symmetry, using Herschel data from the WISH program. Methods. We used HIFI maps of the 987 GHz H2O 202–111 emission to measure the sizes and shapes of 19 high-mass protostellar envelopes. To identify infall, we used HIFI spectra of the optically thin C18O 9–8 and H 218 $_2^{18}$ 2 18 O 111–000 lines. The high-J C18O line traces the warm central material and redshifted H 218 $_2^{18}$ 2 18 O 111–000 absorption indicates material falling onto the warm core. We probe small-scale chemical differentiation by comparing H2O 752 and 987 GHz spectra with those of H 218 $_2^{18}$ 2 18 O. Results. Our measured radii of the central part of the H2O 202–111 emission are 30–40% larger than the predictions from spherical envelope models, and axis ratios are <2, which we consider good agreement. For 11 of the 19 sources, we find a significant redshift of the H 218 $_2^{18}$ 2 18 O 111–000 line relative to C18O 9–8. The inferred infall velocities are 0.6–3.2 km s−1, and estimated mass inflow rates range from 7 × 10−5 to 2 × 10−2M⊙ yr−1. The highest mass inflow rates seem to occur toward the sources with the highest masses, and possibly the youngest ages. The other sources show either expanding motions or H 218 $_2^{18}$ 2 18 O lines in emission. The H 218 $_2^{18}$ 2 18 O 111–000 line profiles are remarkably similar to the differences between the H2O 202–111 and 211–202 profiles, suggesting that the H 218 $_2^{18}$ 2 18 O line and the H2O 202–111 absorption originate just inside the radius where water evaporates from grains, typically 1000–5000 au from the center. In some sources, the H 218 $_2^{18}$ 2 18 O line is detectable in the outflow, where no C18O emission is seen. Conclusions. Together, the H 218 $_2^{18}$ 2 18 O absorption and C18O emission profiles show that the water abundance around high-mass protostars has at least three levels: low in the cool outer envelope, high within the 100 K radius, and very high in the outflowing gas. Thus, despite the small regions, the combination of lines presented in this work reveals systematic inflows and chemical information about the outflows. [ABSTRACT FROM AUTHOR]

Aims: Following our past study of the distribution of warm gas in the G327.3-0.6 massive star-forming region, we aim here at characterizing the large-scale distribution of water in this active region of massive star formation made of individual objects in different evolutionary phases. We investigate possible variations of the water abundance as a function of evolution. Methods: We present Herschel/PACS (4'× 4') continuum maps at 89 and179 µm encompassing the whole region (Hii region and the infrared dark cloud, IRDC) and an APEX/SABOCA (2'× 2') map at 350 µm of the IRDC. New spectral Herschel/HIFI maps toward the IRDC region covering the low-energy water lines at 987 and 1113 GHz (and their H218O counterparts) are also presented and combined with HIFI pointed observations toward the G327 hot core region. We infer the physical properties of the gas through optical depth analysis and radiative transfer modeling of the HIFI lines. Results: The distribution of the continuum emission at 89 and 179 µm follows the thermal continuum emission observed at longer wavelengths, with a peak at the position of the hot core and a secondary peak in the Hii region, and an arch-like layer of hot gas west of this Hii region. The same morphology is observed in the p-H2O 111-000 line, in absorption toward all submillimeter dust condensations. Optical depths of approximately 80 and 15 are estimated and correspond to column densities of 1015 and 2 × 1014 cm-2, respectively, for the hot core and IRDC position. These values indicate an abundance of water relative to H2 of 3 × 10-8 toward the hot core, while the abundance of water does not change along the IRDC with values close to some 10-8. Infall (over at least 20") is detected toward the hot core position with a rate of 1-1.3 × 10-2M⊙/yr, high enough to overcome the radiation pressure that is due to the stellar luminosity. The source structure of the hot core region appears complex, with a cold outer gas envelope in expansion, situated between the outflow and the observer, extending over 0.32 pc. The outflow is seen face-on and rather centered away from the hot core. Conclusions: The distribution of water along the IRDC is roughly constant with an abundance peak in the more evolved object, that is, in the hot core. These water abundances are in agreement with previous studies in other massive objects and chemical models. [ABSTRACT FROM AUTHOR]

Aims. We report the first detection of the J = 1-0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. Methods. This detection occurred as part of an unbiased spectral survey of this object in the 0:8-3 mm range, performed with the IRAM 30 m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. Results. The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4 × 1011 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10-6 for CF+/C+, we derive a total number of C+ of 1.2×1053 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not effcient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Conclusions. Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core. [ABSTRACT FROM AUTHOR]

Context. The earliest phases of high-mass star formation are poorly understood. Aims. Our goal is to determine the physical conditions and kinematic structure of massive starforming cloud clumps. Methods. We analyse H2O 557 GHz line profiles observed with HIFI toward four positions in two infrared-dark cloud clumps. By comparison with ground-based C17O, N2H+, CH3OH, and NH3 line observations, we constrain the volume density and kinetic temperature of the gas and estimate the column density and abundance of H2O and N2H+. Results. The observed water lines are complex with emission and absorption components. The absorption is redshifted and consistent with a cold envelope, while the emission is interpreted as resulting from proto-stellar outflows. The gas density in the clumps is ∼107 cm-3. The o-H2O outflow column density is 0.3-3.0 × 1014 cm-2. The o-H2O absorption column density is between 1.5 × 1014 and 2:6 × 1015 cm-2 with cold o-H2O abundances between 1.5 × 10-9 and 3.1 × 10-8. Conclusions. All clumps have high gas densities (∼107 cm-3) and display infalling gas. Three of the four clumps have outflows. The clumps form an evolutionary sequence as probed by H2O N2H+, NH3, and CH3OH. We find that G28-MM is the most evolved, followed by G11-MM and then G28-NH3. The least evolved clump is G11-NH3 which shows no signposts of starformation; G11-NH3 is a high-mass pre-stellar core. [ABSTRACT FROM AUTHOR]

Aims. Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J 12CO and 13CO observations. Methods. We present APEX 12CO(6-5), (7-6), 13CO(6-5), (8-7) and HIFI 13CO(10-9) maps of the star forming region G327.36-0.6 with a linear size of ~3 pc × 4 pc. We infer the physical properties of the emitting gas on large scales through a local thermodynamic equilibrium analysis, while we apply a more sophisticated large velocity gradient approach on selected positions. Results. Maps of all lines are dominated in intensity by the photon dominated region around the Hii region G327.3-0.5. Mid-J 12CO emission is detected over the whole extent of the maps with excitation temperatures ranging from 20 K up to 80 K in the gas around the Hii region, and H2 column densities from few 1021 cm-2 in the inter-clump gas to 3 × 1022 cm-2 towards the hot core G327.3-0.6. The warm gas (traced by 12 and 13CO(6-5) emission) is only a small percentage (~10%) of the total gas in the infrared dark cloud, while it reaches values up to ~35% of the total gas in the ring surrounding the Hii region. The 12CO ladders are qualitatively compatible with photon dominated region models for high density gas, but the much weaker than predicted 13CO emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50''(~0.8 pc), implying that the mid-J 12CO and 13CO inter-clump emission is due to high density components with low filling factor. Finally, the detection of the 13CO(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone. [ABSTRACT FROM AUTHOR]

Aims. We present Herschel-HIFI observations of 14 water lines in W43-MM1, a massive protostellar object in the luminous star-cluster-forming region W43. We place our study in the more general context of high-mass star formation. The dynamics of these regions may be represented by either the monolithic collapse of a turbulent core, or competitive accretion. Water turns out to be a particularly good tracer of the structure and kinematics of the inner regions, allowing an improved description of the physical structure of the massive protostar W43-MM1 and an estimation of the amount of water around it. Methods. We analyze the gas dynamics from the line profiles using Herschel-HIFI observations acquired as part of the Water In Star-forming regions with Herschel project of 14 far-IR water lines (H216O, H217O, H218O), CS(11-10), and C18O(9-8) lines, using our modeling of the continuum spectral energy distribution. The spectral modeling tools allow us to estimate outflow, infall, and turbulent velocities and molecular abundances. We compare our results to previous studies of low-, intermediate-, and other high-mass objects. Results. As for lower-mass protostellar objects, the molecular line profiles are a mix of emission and absorption, and can be decomposed into "medium" (full width at half maximum FWHM ≃ 5-10 km s-1), and "broad" velocity components (FWHM ≃ 20-35 km s-1). The broad component is the outflow associated with protostars of all masses. Our modeling shows that the remainder of the water profiles can be well-fitted by an infalling and passively heated envelope, with highly supersonic turbulence varying from 2.2 km s-1 in the inner region to 3.5 km s-1 in the outer envelope. In addition, W43-MM1 has a high accretion rate of between 4.0 × 10-4 and 4.0 × 10-2 M☉ yr-1, as derived from the fast (0.4-2.9 km s-1) infall observed. We estimate a lower mass limit for gaseous water of 0.11 M☉ and total water luminosity of 1.5 L☉ (in the 14 lines presented here). The central hot core is detected with a water abundance of 1.4 × 10-4, while the water abundance for the outer envelope is 8 × 10-8. The latter value is higher than in other sources, and most likely related to the high turbulence and the micro-shocks created by its dissipation. Conclusions. Examining the water lines of various energies, we find that the turbulent velocity increases with the distance from the center. While not in clear disagreement with the competitive accretion scenario, this behavior is predicted by the turbulent core model. Moreover, the estimated accretion rate is high enough to overcome the expected radiation pressure. [ABSTRACT FROM AUTHOR]

Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims. The first systematic survey of spectrally resolved water emission in 29 low-mass (L <40 Lʘ) protostellar objects is presented. The sources cover a range of luminosities and evolutionary states. The aim is to characterise the line profiles to distinguish physical components in the beam and examine how water emission changes with protostellar evolution. Methods. H2O was observed in the ground-slate 110-101 transition at 557 GHz (Eup/kB -∼ 60K) as single-point observations with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel in 29 deeply embedded Class 0 and I low-mass protostars. Complementary far-R and tub-mm continuum data (including PACS data from our programme) are used to constrain the spectral energy distribution (SED) of each source. H20 intensities are compared to inferred envelope properties, e.g., mass and density, outflow properties and CO 3-2 emission. Results. H2O emission is detected in all objects except one (TMCIA). The line profiles are complex and consist of several kinematic components tracing different physical regions in each system. In particular, the profiles are typically dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows, not in the quiescent envelope. Several sources show multiple shock components appearing in either emission or absorption, thus constraining the internal geometry of the system. Furthermore, the components include inverse P-Cygni profiles in seven sources (nix Class 0, one Class 1) indicative of infalling envelopes, and regular P-Cygni profiles in four sources (three Class 1, one Class 0) indicative of expanding envelopes. Molecular "bullets" moving at ≳50 km s-1 with respect to the source are detected in four Class 0 sources; three of these sources were not known to harbour bullets previously. In the outflow, the H2O/CO abundance ratio an a function of velocity in nearly the name for all line wings, increasing from 10-3 at low velocities (<5 km s-1) to ≳ 10-1 at high velocities (>10 km s-1). The water abundance in the outer cold envelope in low, ≳10-10. The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission in dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears. [ABSTRACT FROM AUTHOR]

We present the first paper in a series detailing the results of 13CO observations of a ∼1 deg2 region of the giant molecular cloud (GMC) complex associated with the H ii region RCW 106. The 13CO observations are also the first stage of a multimolecular line study of the same region. These observations were amongst the first made using the new on-the-fly mapping capability of the Australia Telescope National Facility Mopra Telescope. In the configuration used, the instrument provided a full width at half-maximum (FWHM) beam size of 33 arcsec and a velocity resolution of 0.17 km s−1. The gas emission takes the form of a string of knots, oriented along an axis that extends from the north-west (NW) to the south-east (SE) of the field of the observations, and which is surrounded by a more extended, diffuse emission. We analyse the 2D integrated 13CO emission using theclumpfind algorithm and identify 61 clumps. We compare the gas data in the GMC with the dust data provided by 21-μm Midcourse Space Experiment ( MSX) and 1.2-mm Swedish European Southern Observatory Submillimetre Telescope (SEST) images that we both regridded to the cell spacing of the Mopra data and smoothed to the same resolution. The 13CO emission is more diffuse and extended than the dust emission revealed at the latter two wavebands, which both have a much higher contrast between the peaks and the extended emission. From comparison of their centre positions, we find that only ∼50 per cent of the 13CO clump fits to the data are associated with any dust clumps. Using the clump fits, the total local thermodynamic equilibrium gas mass above the 3σ level measured from the molecular data is , whereas that measured from the smoothed 1.2-mm SEST dust data is . [ABSTRACT FROM AUTHOR]