Massive Star Formation Research Papers (original) (raw)

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- Radio Astronomy, Infrared Astronomy, HII Regions, Low Frequency

How mass is accumulated from cloud-scale down to individual stars is a key open question in understanding high-mass star formation. Here, we present the mass accumulation process in a hub-filament cloud G22 that is composed of four supercritical filaments. Velocity gradients detected along three filaments indicate that they are collapsing with a total mass infall rate of about 440 M e Myr −1 , suggesting the hub mass would be doubled in six free-fall times, adding up to ∼2 Myr. A fraction of the masses in the central clumps C1 and C2 can be accounted for through large-scale filamentary collapse. Ubiquitous blue profiles in HCO + (3–2) and 13 CO(3–2) spectra suggest a clump-scale collapse scenario in the most massive and densest clump C1. The estimated infall velocity and mass infall rate are 0.31 km s −1 and 7.2×10 −4 M e yr −1 , respectively. In clump C1, a hot molecular core (SMA1) is revealed by the Submillimeter Array observations and an outflow-driving high-mass protostar is located at the center of SMA1. The mass of the protostar is estimated to be 11–15 M e and it is still growing with an accretion rate of 7×10 −5 M e yr −1. The coexistent infall in filaments, clump C1, and the central hot core in G22 suggests that pre-assembled mass reservoirs (i.e., high-mass starless cores) may not be required to form high-mass stars. In the course of high-mass star formation, the central protostar, the core, and the clump can simultaneously grow in mass via core-fed/disk accretion, clump-fed accretion, and filamentary/cloud collapse.

We have used the well-selected sample of ∼1750 embedded, young, massive stars identified by the Red MSX Source (RMS) survey to investigate the Galactic distribution of recent massive star formation. We present molecular line observations for ∼800 sources without existing radial velocities. We describe the various methods used to assign distances extracted from the literature and solve the distance ambiguities towards approximately 200 sources located within the solar circle using archival H I data. These distances are used to calculate bolometric luminosities and estimate the survey completeness (∼2 × 104 L⊙). In total, we calculate the distance and luminosity of ∼1650 sources, one third of which are above the survey’s completeness threshold. Examination of the sample’s longitude, latitude, radial velocities and mid-infrared images has identified ∼120 small groups of sources, many of which are associated with well-known star formation complexes, such as G305, G333, W31, W43, W49 and W51. We compare the positional distribution of the sample with the expected locations of the spiral arms, assuming a model of the Galaxy consisting of four gaseous arms. The distribution of young massive stars in the Milky Way is spatially correlated with the spiral arms, with strong peaks in the source position and luminosity distributions at the arms’ Galactocentric radii. The overall source and luminosity surface densities are both well correlated with the surface density of the molecular gas, which suggests that the massive star formation rate per unit molecular mass is approximately constant across the Galaxy. A comparison of the distribution of molecular gas and the young massive stars to that in other nearby spiral galaxies shows similar radial dependences. We estimate the total luminosity of the embedded massive star population to be ∼0.76 × 108 L⊙, 30 per cent of which is associated with the 10 most active star-forming complexes. We measure the scaleheight as a function of the Galactocentric distance and find that it increases only modestly from ∼20–30 pc between 4 and 8 kpc, but much more rapidly at larger distances.

- by James Urquhart
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- Massive Star Formation
- by Christine Fleener and +1
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- Massive Star Formation
- by Dr. Kamal Kumar Tanti
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- Massive Star Formation

We have carried out a multiwavelength study of the infrared dust bubble N6 to extensively investigate the molecular environs and star-forming activities therein. Mapping observations in 12^{12}12CO J = 1-0 and 13^{13}13CO J = 1-0 performed with the Purple Mountain Observatory 13.7 m telescope have revealed four velocity components. Comparison between distributions of each component and the infrared emission suggests that three components are correlated with N6. There are 10 molecular clumps detected. Among them, five have reliable detections in both 12^{12}12CO and 13^{13}13CO and have similar LTE and non-LTE masses ranging from 200 to higher than 5000 M ⊙_{⊙}⊙. With larger gas masses than virial masses, these five clumps are gravitationally unstable and have the potential to collapse to form new stars. The other five clumps are only reliably detected in 12^{12}12CO and have relatively small masses. Five clumps are located on the border of the ring structure, and four of them are elongated along the shell. This is well in agreement with the collect-and-collapse scenario. The detected velocity gradient reveals that the ring structure is still under expansion owing to stellar winds from the exciting star(s). Furthermore, 99 young stellar objects (YSOs) have been identified based on their infrared colors. A group of YSOs reside inside the ring, indicating active star formation in N6. Although no confirmative features of triggered star formation are detected, the bubble and the enclosed H II region have profoundly reconstructed the natal cloud and altered the dynamics therein.

- by Jinghua Yuan and +1
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- Infrared Astronomy, Interstellar Medium, Star Formation, Massive Star Formation

Using the 870 μm APEX Telescope large area survey of the Galaxy, we have identified 577 submillimetre continuum sources with masers from the methanol multibeam survey in the
◦◦◦
region280 <l<20;|b|<1.5.94percentofmethanolmasersintheregionareassociated with submillimetre dust emission. We estimate masses for ∼450 maser-associated sources and find that methanol masers are preferentially associated with massive clumps. These clumps are centrally condensed, with envelope structures that appear to be scale-free, the mean maser position being offset from the peak column density by 0 ± 4 arcsec. Assuming a Kroupa initial mass function and a star formation efficiency of ∼30 per cent, we find that over two-thirds of the clumps are likely to form clusters with masses >20 M⊙. Furthermore, almost all clumps satisfy the empirical mass–size criterion for massive star formation. Bolometric luminosities taken from the literature for ∼100 clumps range between ∼100 and 106 L⊙. This confirms the link between methanol masers and massive young stars for 90 per cent of our sample. The Galactic distribution of sources suggests that the star formation efficiency is significantly reduced in the Galactic Centre region, compared to the rest of the survey area, where it is broadly constant, and shows a significant drop in the massive star formation rate density in the outer Galaxy. We find no enhancement in source counts towards the southern Scutum– Centaurus arm tangent at l ∼ 315◦, which suggests that this arm is not actively forming stars.

- by James Urquhart
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- Massive Star Formation

We report the discovery based on GLIMPSE data of a proto-stellar system driving a bipolar outflow. The bipolar outflow closely resembles the shape of an hourglass in the infrared. The total luminosity of L$_{total}$ = 5507 L$_{⊙}$, derived from IRAS fluxes, indicates the ongoing formation of a massive star in this region. The spectral energy distribution (SED) of the driving source is fitted with an online SED fitting tool, which results in a spectral index of about 1.2. This, along with the presence of a bipolar outflow, suggests the detection of a Class I protostar. The driving source indicates prominent infrared excesses in color-color diagrams based on archived 2 MASS and GLIMPSE data, which is in line with an early evolutionary stage of the system.

- by Jinghua Yuan and +1
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- Interstellar Medium, Star Formation, Massive Star Formation, Interstellar Medium and Star formation

We report the results of 870-μm continuum observations, using the Large APEX Bolometer Camera, towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol MultiBeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with compact dense clumps identified from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99 per cent for the full MMB catalogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find median clump masses of a few 103 M⊙ and that all but a handful of sources satisfy the mass–size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ∼2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.

- by James Urquhart
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- Massive Star Formation
- by E. Caux
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- Interstellar Medium, Astrochemistry, Massive Star Formation, Interstellar molecules
- by Charles Figura
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- Massive Star Formation

In this paper, we report on the discovery of an O2 If*/WN6 star probably still partially embedded in its parental cocoon in the starburst cluster NGC 3603. From the observed size of the associated compact HII region, it has been possible to derive a probable dynamic age of no more than 600 000 yr. Using the computed visual extinction value AV ∼ 6.0 ± 0.2 mag, an absolute visual magnitude MV = −5.7 mag has been obtained. For the assumed heliocentric distance of 7.6 kpc, this results in a bolometric luminosity of 8 × 105 L. Also, from the V magnitude and the V − I colour of the new star, and from previous models for the massive star population of NGC 3603, we estimate the mass of the binary (O2 If*/WN6 + O3 If) and the single star (O2 If*/WN6). For the binary, we find that the initial masses of each component possibly exceed 80 and 40 M, respectively, while for the single star the initial mass of MTT58 is possibly in excess of 100 M.

We present the Red MSX Source survey, the largest statistically selected catalog of young massive protostars and H ii regions to date. We outline the construction of the catalog using mid- and near-infrared color selection. We also discuss the detailed follow up work at other wavelengths, including higher spatial resolution data in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcsec. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole; we find evidence that the most massive stars form: (1) preferentially nearer the Galactic center than the anti-center; (2) in the most heavily reddened environments, suggestive of high accretion rates; and (3) from the most massive cloud cores.

- by James Urquhart
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- Massive Star Formation, Galactic Structure

We present a complete sample of molecular clumps containing compact and ultracompact HII (UC HII) regions between l = 10◦ and 60◦ and |b| < 1◦, identified by combining the APEX Telescope Large Area Survey of the Galaxy submm and CORNISH radio continuum surveys with visual examination of archival infrared data. Our sample is complete to optically thin, compact and UC H II regions driven by a zero-age main-sequence star of spectral type B0 or earlier embedded within a 1000M⊙ clump. In total we identify 213 compact and UC H II regions, associated with 170 clumps. Unambiguous kinematic distances are derived for these clumps and used to estimate their masses and physical sizes, as well as the Lyman continuum fluxes and sizes of their embedded H II regions. We find a clear lower envelope for the surface density of molecular clumps hosting massive star formation of 0.05 g cm−2 , which is consistent with a similar sample of clumps associated with 6.7 GHz masers. The mass of the most massive embedded stars is closely correlated with the mass of their natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by current stellar atmosphere models. The properties of clumps associated with compact and UC H II regions are very similar to those associated with 6.7 GHz methanol masers and we speculate that there is little evolution in the structure of the molecular clumps between these two phases. Finally, we identify a significant peak in the surface density of compact and UC H II-regions associated with the W49A star-forming complex, noting that this complex is truly one of the most massive and intense regions of star formation in the Galaxy.

- by James Urquhart
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- Massive Star Formation

Context. The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) is the largest and most sensitive systematic survey of the inner Galactic plane in the submillimetre wavelength regime. The observations were carried out with the Large APEX Bolometer Camera (LABOCA), an array of 295 bolometers observing at 870 μm (345 GHz).
Aims. In this research note we present the compact source catalogue for the 280◦ < l < 330◦ and 21◦ < l < 60◦ regions of this survey. Methods. The construction of this catalogue was made with the source extraction routine SExtractor using the same input parame- ters and procedures as used to analyse the inner Galaxy region presented in an earlier publication (i.e., 330◦ < l < 21◦ ).
Results. We have identified 3523 compact sources and present a catalogue of their properties. When combined with the regions al- ready published, this provides a comprehensive and unbiased database of ∼10 163 massive, dense clumps located across the inner Galaxy.

- by James Urquhart
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- Massive Star Formation