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Identifying infall motions is crucial for our understanding of accretion processes in regions of star formation. The NH3 (1,1) hyperfine intensity anomaly (HIA) has been proposed to be a readily usable tracer for such infall motions in star-forming regions harboring young stellar objects at very early evolutionary stages. In this paper, we seek to study the HIA toward 15 infall candidate regions in order to assess its reliability as an infall tracer. Using deep observations of the NH3 (1, 1) transition with the Effelsberg 100 m telescope, we identified HIAs toward all 15 targets. Of the 15 sources, 14 exhibit anomalous intensities in either the inner or outer satellite lines. All the derived HIAs conform to the framework of the existing two models, namely hyperfine selective trapping (HST) and systematic contraction or expansion motion (CE) models. In our sample of infall candidates, the majority of the HIAs remain consistent with the HST model. Only in three targets are the HIAs consistent with infall motions under the CE model. Thus, the HIA could indeed be used as an infall tracer, but does not appear to be highly sensitive to infall motions in our single-dish data. Nevertheless, the emission could be blended with emission from outflow activities. HIAs consistent with the HST model show stronger anomalies with increasing kinetic temperatures (TK), which is expected based on the HST model. On the other hand, HIAs consistent with infall motions show little dependence on Tk. Therefore, HIAs may preferably trace the infall of cold gas. [ABSTRACT FROM AUTHOR]

Context. Together with gravity, turbulence, and stellar feedback, magnetic fields (B-fields) are thought to play a critical role in the evolution of molecular clouds and star formation processes. The polarization of thermal dust emission is a popular tracer of B-fields in star-forming regions. Aims. We aim to map the morphology and measure the strength of B-fields of the nearby molecular cloud, rho Ophiuchus-A (ρ Oph-A), to understand the role of B-fields in regulating star formation and in shaping the cloud. Methods. We analyzed the far-infrared (FIR) polarization of thermal dust emission observed by SOFIA/HAWC+ at 89 and 154 μm toward the densest part of ρ Oph-A, which is irradiated by the nearby B3/4 star, Oph-S1. These FIR polarimetric maps cover an area of ~4.5′ × 4.5′ (corresponding to 0″.18 × 0″.18 pc2) with an angular resolution of 7.8″ and 13.6″ respectively. Results. The ρ Oph-A cloud exhibits well-ordered B-fields with magnetic orientations that are mainly perpendicular to the ridge of the cloud toward the densest region. We obtained a map of B-field strengths in the range of 0.2–2.5 mG, using the Davis-Chandrasekhar-Fermi (DCF) method. The B-fields are strongest at the densest part of the cloud, which is associated with the starless core SM1, and then decrease toward the outskirts of the cloud. By calculating the map of the mass-to-flux ratio, Alfvén Mach number, and plasma β parameter in ρ Oph-A, we find that the cloud is predominantly magnetically sub-critical, sub-Alfvénic, which implies that the cloud is supported by strong B-fields that dominate over gravity, turbulence, and thermal gas energy. The measured B-field strengths at the two densest subsregions using other methods that account for the compressible mode are relatively lower than that measured with the DCF method. However, these results do not significantly change our conclusions on the roles of B-fields relative to gravity and turbulence on star formation. Our virial analysis suggests that the cloud is gravitationally unbound, which is consistent with the previous detection of numerous starless cores in the cloud. By comparing the magnetic pressure with the radiation pressure from the Oph-S1 star, we find that B-fields are sufficiently strong to support the cloud against radiative feedback and to regulate the shape of the cloud. [ABSTRACT FROM AUTHOR]

Context. The Lagoon Nebula (M8) is host to multiple regions with recent and ongoing massive star formation, due to which it appears as one of the brightest H II regions in the sky. M8-Main and M8 East, two prominent regions of massive star formation, have been studied in detail over the past few years, while large parts of the nebula and its surroundings have received little attention. These largely unexplored regions comprise a large sample of molecular clumps that are affected by the presence of massive O- and B-type stars. Thus, exploring the dynamics and chemical composition of these clumps will improve our understanding of the feedback from massive stars on star-forming regions in their vicinity. Aims. We established an inventory of species observed towards 37 known molecular clumps in M8 and investigated their physical structure. We compared our findings for these clumps with the galaxy-wide sample of massive dense clumps observed as part of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). Furthermore, we investigated the region for signs of star formation and stellar feedback. Methods. To obtain an overview of the kinematics and chemical abundances across the sample of molecular clumps in the M8 region, we conducted an unbiased line survey for each clump. We used the Atacama Pathfinder EXperiment (APEX) 12m submillimetre telescope and the 30 m telescope of the Institut de Radioastronomie Millimétrique (IRAM) to conduct pointed on-off observations of 37 clumps in M8. These observations cover bandwidths of 53 GHz and 40 GHz in frequency ranges from 210 GHz to 280 GHz and from 70 GHz to 117 GHz, respectively. Temperatures were derived from rotational transitions of acetonitrile, methyl acetylene, and para-formaldehyde. Additional archival data from the Spitzer, Herschel, MSX, APEX, WISE, JCMT, and AKARI telescopes were used to investigate the morphology of the region and to derive the physical parameters of the dust emission by fitting spectral energy distributions to the observed flux densities. Results. Across the observed M8 region, we identify 346 transitions from 70 different molecular species, including isotopologues. While many species and fainter transitions are detected exclusively towards M8 East, we also observe a large chemical variety in many other molecular clumps. We detect tracers of photo-dissociation regions (PDRs) across all the clumps, and 38% of these clumps show signs of star formation. In our sample of clumps with extinctions between 1 and 60 mag, we find that PDR tracers are most abundant in clumps with relatively low H2 column densities. When comparing M8 clumps to ATLASGAL sources at similar distances, we find them to be slightly less massive (median 10 M⊙) and have compatible luminosities (median 200 L⊙) and radii (median 0.16 pc). In contrast, dust temperatures of the clumps in M8 are found to be increased by approximately 5 K (25%), indicating substantial external heating of the clumps by radiation of the present O- and B-type stars. Conclusions. This work finds clear and widespread effects of stellar feedback on the molecular clumps in the Lagoon Nebula. While the radiation from the O- and B-type stars possibly causes fragmentation of the remnant gas and heats the molecular clumps externally, it also gives rise to extended PDRs on the clump surfaces. Despite this fragmentation, the dense cores within 38% of the observed clumps in M8 are forming a new generation of stars. [ABSTRACT FROM AUTHOR]

Protostellar jets and outflows are essential ingredients of the star formation process. A better understanding of this phenomenon is important in its own right as well as for many fundamental aspects of star formation. Jets and outflows associated with O-type protostars are rarely studied with observations reaching the close vicinity of the protostars. In this work, we report high-resolution ALMA and VLBA observations to reveal a clear and consistent picture of an outflow associated with an O-type protostar candidate in the G26.50+0.28 region. These observations reveal, for the first time, a collimated jet located in the middle of the outflow cavity. The jet is found to be perpendicular to an elongated disk/toroid and its velocity gradient. The collimated jet appears to show a small amplitude (α≈0°.06) counterclockwise precession, when looking along the blueshifted jet axis from the strongest continuum source MM1, with a precession length of 0.22 pc. The inclination of the jet is likely to be very low (≈8°), which makes it a promising target to study its transverse morphologies and kinematics. However, no clear evidence of jet rotation is found in the ALMA and VLBA observations. The three-dimensional velocities of the water maser spots appear to show the same absolute speed with respect to different opening angles, suggesting the jet winds may be launched in a relatively small region. This favors the X-wind model, that is, jets are launched in a small area near the inner disk edge. [ABSTRACT FROM AUTHOR]

We report a measurement of the trigonometric parallax of 22 GHz water masers in the massive star-forming region G034.43+0.24 as part of the Bar and Spiral Structure Legacy Survey using the Very Long Baseline Array. The parallax is 0.330 ± 0.018 mas, corresponding to a distance of 3.03 − 0.16 + 0.17 kpc. This locates G034.43+0.24 near the inner edge of the Sagittarius spiral arm and at one end of a linear distribution of massive young stars that cross nearly the full width of the arm. The measured three-dimensional motion of G034.43+0.24 indicates a near-circular Galactic orbit. The water masers display arc-like distributions, possibly bow shocks, associated with winds from one or more massive young stars. [ABSTRACT FROM AUTHOR]

We mapped the kinetic temperature structure of Orion KL in a ∼20″ (∼8000 au) sized region with para-H2CS 707 − 606, 726 − 625, and 725 − 624 making use of Atacama Large Millimeter/submillimeter Array Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1.″65 × 1.″14 (∼550 au) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H2CS 726 − 625/707 − 606 and 725 − 624/707 − 606 with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H2CS line ratios at a spatial density of 107 cm−3, are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event which occurred several hundred years ago and greatly affected the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas. [ABSTRACT FROM AUTHOR]

Context. Fragmentation and feedback are two important processes during the early phases of star formation. Aims. Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby H ii regions. Methods. We present a high angular resolution study of a sample of massive proto-cluster clumps G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71. Combining infrared data at 4.5, 8.0, 24, and 70 μm, we use a few arcsecond resolution, radiometer and millimeter inteferometric data taken at 1.3 cm, 3.5 mm, 1.3 mm, and 870 μm to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring H ii regions. Taking advantage of that, we tested triggered star formation using a novel method where we study the alignment of the center of mass traced by dust emission at multiple scales. Results. The eight massive clumps, identified based on single-dish observations, have masses ranging from 228 to 2279 M⊙ within an effective radius of Reff ~ 0.5 pc. We detect compact structures towards six out of the eight clumps. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff ~ 0.02 pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8 M⊙ at a small scale of Reff ~ 0.02 pc. We find that the two infrared quiet clumps with the lowest mass and lowest surface density with <300 M⊙ do not host any compact sources, calling into question their ability to form high-mass stars. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1 pc). Conclusions. We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired. [ABSTRACT FROM AUTHOR]

Isocyanic acid (HNCO), the most stable of the simplest molecules containing the four main elements essential for organic chemistry, has been observed in several astrophysical environments such as molecular clouds, star-forming regions, external galaxies, and comets. In this work, we model HNCO spectral line profiles towards the low-mass solar type protostar IRAS 16293−2422 observed with the ALMA interferometer, the IRAM, JCMT, and APEX single-dish radio telescopes, and the HIFI instrument on board the Herschel Space Observatory. In star-forming environments, the HNCO emission is not always in Local Thermodynamical Equilibrium (LTE). A non-LTE radiative transfer approach is necessary to properly interpret the line profiles, and accurate collisional rate coefficients are needed. Here, we used the radex package with a completely new set of collisional quenching rates between HNCO and both ortho-H2 and para-H2 obtained from quantum chemical calculations yielding a novel potential energy surface in the rigid rotor approximation. We find that the lines profiles towards IRAS 16293−2422 are very well reproduced if we assume that the HNCO emission arises from a compact, dense, and hot physical component associated with the hot corino, a warm component associated with the internal part of the protostellar envelope, and a cold and more extended component associated with the outer envelope. The derived HNCO abundances from our model agree well with those computed with the Nautilus chemical code. [ABSTRACT FROM AUTHOR]

Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relationship between the star formation rate and the mass of dense gas available for star formation. Validation of such trends requires the establishment of reliable methods to trace the dense gas in galaxies. One frequent assumption is that the HCN (J = 1-0) transition is unambiguously associated with gas at H2 densities ≫ 104 cm-3. If so, the mass of gas at densities ≫ 104 cm-3 could be inferred from the luminosity of this emission line, LHCN (1-0). Here we use observations of the Orion A molecular cloud to show that the HCN (J = 1-0) line traces much lower densities ~ 103 cm-3 in cold sections of this molecular cloud, corresponding to visual extinctions AV ≈ 6 mag. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain LHCN (1-0) in star forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100 GHz (also including 12CO, 13CO, C18O, CN, and CCH), N2H+ is the only species clearly associated with relatively dense gas. [ABSTRACT FROM AUTHOR]

Context. Filamentary structures are ubiquitous in the interstellar medium. Investigating their connection to the large-scale structure of the Galaxy and their role in star formation is leading to a paradigm shift in our understanding of star formation. Aims. We study the properties of filamentary structures from the ATLASGAL survey, which is the largest and most sensitive systematic ground-based survey of the inner Galactic plane at submillimeter wavelengths. Methods. We use the DisPerSE algorithm to identify spatially coherent structures located across the inner-Galaxy (300° < l < 60° and |b| < 1.5). As a result we produce a catalogue of ~1800 structures; these were then independently classified by the five lead authors into one of the following types: marginally resolved, elongated structures, filaments, network of filaments and complexes. This resulted in the identification of 517 filamentary structures. We determine their physical properties and investigate their overall Galactic distribution. Results. We find that almost 70% of the total 870 µm flux associated with these structures resides in filaments and networks of filaments and we estimate that they are likely to be associated with a similar fraction of the mass. Correlating these structures with tracers of massive star formation we also find that a similar fraction of the massive star forming clumps are associated with filaments and networks of filaments, which highlights the importance of these types of structures to star formation in the Galaxy. We have determined distances, masses and physical sizes for 241 of the filamentary structures. We find a median distance of 3.8 kpc, a mean mass of a few 10³ M⊙, a mean length of ~6 pc and a mass-to-length ratio of (M/L) ~200-2000 M⊙ pc-1. We also find that these filamentary structures are tightly correlated with the spiral arms in longitude and velocity, and that their semi-major axis is preferentially aligned parallel to the Galactic mid-plane and therefore with the direction of large-scale Galactic magnetic field. We find many examples where the dense filaments identified in ATLASGAL are associated with larger scale filamentary structures (~100 pc), and argue that this is likely to be common, and as such these may indicate a connection between large-scale Galactic dynamics and star formation. Conclusions. We have produced a large and Galaxy-wide catalogue of dense filamentary structures that are representative of a particular size and mass range not previously well studied in the literature. Analyses of the properties and distribution of these filaments reveals that they are correlated with the spiral arms and make a significant contribution to star formation in the Galaxy. Massive star formation is ongoing within ~20% of the filaments and is strongly correlated with the filaments with the largest mass-to-length ratios. The luminosity of the embedded sources has a similar distribution to the Galactic-wide samples of young massive stars and can therefore be considered to be representative. [ABSTRACT FROM AUTHOR]

We present the G-virial method which aims to quantify (1) the importance of gravity in molecular clouds in the position-positionvelocity (PPV) space; and (2) properties of the gas condensations in molecular clouds. Different from previous approaches that calculate the virial parameter for different regions, our new method takes gravitational interactions between all the voxels in 3D PPV data cubes into account, and generates maps of the importance of gravity. This map can be combined with the original data cube to derive relations such as the mass-radius relation. Our method is important for several reasons. First, it offers the ability to quantify the centrally condensed structures in the 3D PPV data cubes, and enables us to compare them in an uniform framework. Second, it allows us to understand the importance of gravity at different locations in the data cube, and provides a global picture of gravity in clouds. Third, it offers a robust approach to decomposing the data into different regions which are gravitationally coherent. To demonstrate the application of our method we identified regions from the Perseus and Ophiuchus molecular clouds, and analyzed their properties. We found an increase in the importance of gravity towards the centers of the individual molecular condensations. We also quantified the properties of the regions in terms of mass-radius and mass-velocity relations. Through evaluating the virial parameters based on the G-virial, we found that all our regions are almost gravitationally bound. Cluster-forming regions appear are more centrally condensed. [ABSTRACT FROM AUTHOR]

The formation of hypercompact (HC) H II regions is an important stage in massive star formation. Spectral line and continuum observations can explore its dynamic conditions. We present high angular resolution observations carried out with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward the HC H II region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected a total of about 25 transitions of 8 different species and their isotopologues (CO, CH3CN, SO2, CH3CCH, OCS, CS, H, and NH3). G35.58-0.03 consists of an HC H II core with electron temperature K, emission measure EM ≈1.9 × 109 pc cm–6, local volume electron density ne = 3.3 × 105 cm–3, and a same width of radio recombination line FWHM ≈ 43.2 km s–1 for both H30α and H38β at its intrinsic core size ∼3714 AU. The H30α line shows evidence of an ionized outflow driving a molecular outflow. Based on the derived Lyman continuum flux, there should be an early-type star equivalent to O6.5 located inside the H II region. From the continuum spectral energy distribution from 3.6 cm, 2.0 cm, 1.3 cm, 1.3 mm and 0.85 mm to 0.45 mm, we distinguished the free-free emission (25% ∼ 55%) from the warm dust component (75% ∼ 45%) at 1.3 mm. The molecular envelope shows evidence of infall and outflow with an infall rate of 0.05 M☼ yr–1 and a mass loss rate of 5.2 × 10–3M☼ yr–1. The derived momentum (∼0.05 M☼ km s–1) is consistent between the infalling and outflowing gas per year. It is suggested that the infall is predominant and the envelope mass of dense core is increasing rapidly, but the accretion in the inner part might already be halted. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158μm fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z = 6.00 quasar SDSS J231038.88+185519.7 using the IRAM facilities. The ALMA observations were carried out in the extended array at 0".7 resolution. We have detected the line and dust continuum in all five objects. The derived [C II] line luminosities are 1.6 × 109 to 8.7 × 109 L☉ and the [C II]-to-FIR luminosity ratios are 2.9-5.1 × 10-4, which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0".3-0".6 (i.e., 1.7-3.5 kpc) for the [C II] line emission and 0".2-0".4 (i.e., 1.2-2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the star-forming gas in the nuclear region. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [Cii]-emitting regions are of order 1010-1011M☉. Given these estimates, the mass ratios between the supermassive black holes and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars. [ABSTRACT FROM AUTHOR]

Accurate techniques that allow for the derivation of the spatial density in star formation regions are rare. A technique that has found application for the derivation of spatial densities in Galactic star formation regions utilizes the density-sensitive properties of the K-doublet transitions of formaldehyde (H2CO). In this paper, we present an extension of our survey of the formaldehyde 110-111 (λ = 6.2 cm) and 211-212 (λ = 2.1 cm) K-doublet transitions of H2CO in a sample of 56 starburst systems. We have extended the number of galaxies in which both transitions have been detected from 5 to 13. We have improved our spatial density measurements by incorporating kinetic temperatures based upon NH3 measurements of 11 of the galaxies with a total of 14 velocity components in our sample. Our spatial density measurements lie in a relatively narrow range from 104.5 to 105.5 cm-3. This implies that the Schmidt-Kennicutt relation between LIR andMdense (1) is an indication of the dense gas mass reservoir available to form stars and (2) is not directly dependent upon a higher average density driving the star formation process in the most luminous starburst galaxies. We have also used our H2CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 102-103, than those derived using HCN. This disparity suggests that H2CO traces a denser, more compact component of the giant molecular clouds in our starburst galaxy sample. We also report measurements of the rotationally excited λ = 6.3 cm2Π1/2J = 1/2 state of OH and the H111α radio recombination line taken concurrently with our H2CO 110-111 measurements. [ABSTRACT FROM AUTHOR]

ABSTRACT We aim at understanding the massive star formation (MSF) limit in the mass-size space of molecular structures recently proposed by Kauffmann & Pillai. As a first step, we build on the property that power-law density profiles for molecular clumps combined with a volume density threshold for the overall star formation naturally leads to mass-radius relations for molecular clumps containing given masses of star-forming gas. Specifically, we show that the mass mclump and radius rclump of molecular clumps whose density profile slope is − p and which contain a mass mth of gas denser than a density threshold ρth obeys the following: . In a second step, we use the relation between the mass of embedded clusters and the mass of their most massive star to estimate the minimum mass of the star-forming gas needed to form a 10-M⊙ star. Assuming a star formation efficiency (SFE) of SFE ≃ 0.30, this gives . In a third step, we demonstrate that, for sensible choices of the clump density index ( p ≃ 1.7) and of the cluster formation density threshold ( nth≃ 104 cm−3), the line of constant in the mass-radius space of molecular structures equates to the MSF limit for spatial scales larger than 0.3 pc. Hence, the observationally inferred MSF limit of Kauffmann & Pillai is consistent with a threshold in star-forming gas mass beyond which the star-forming gas reservoir is large enough to allow the formation of massive stars. For radii smaller than 0.3 pc, the MSF limit is shown to be consistent with the formation of a 10-M⊙ star ( mth, crit≃ 30 M⊙ with SFE ≃ 0.3) out of its individual pre-stellar core of density threshold . The inferred density thresholds for the formation of star clusters and individual stars within star clusters match those previously suggested in the literature. [ABSTRACT FROM AUTHOR]

Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass (∼20 solar masses) young stellar object. The image shows an elongated structure with a size of ∼13 × 19 astronomical units, consistent with a disk seen at an inclination angle of ∼45°. Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system. [ABSTRACT FROM AUTHOR]

There is no generally accepted evolutionary scheme for high mass star formation yet. A simple approach to address this problem is to cover several of the known stages during the formation of massive stars in the same cloud and then investigate their properties trying to construct an evolutionary sequence. Here we present such a project conducted with complementary APEX and ATCA observations. These observations show a compact and bright single hot core in the G327.3-0.6 region on a 0.03 pc scale with a mass of 500 M⊙ and 0.5–1.5 105 L⊙. Additionally a clumpy filament is seen in N2H+. Together with cm continuum observations, the data reveal like pearls on a string several stages of massive star formation, with likely the youngest stages hiding in the cold N2H+ cores analysed with a multilevel study of the APEX and ATCA observations. [ABSTRACT FROM AUTHOR]

We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J = 2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ∼105M☼ to 7 × 105M☼. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24 μm, and Hα narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction. [ABSTRACT FROM AUTHOR]

Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array, we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk. [ABSTRACT FROM AUTHOR]