scholarly journals Physical and chemical structure of dense cores in regions of high mass star formation

2005 ◽  
Vol 1 (S227) ◽  
pp. 92-97 ◽  
Author(s):  
Igor Zinchenko ◽  
Lev Pirogov ◽  
Paola Caselli ◽  
Lars E.B. Johansson ◽  
Sergey Malafeev ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Structure ◽  
High Mass ◽  
Mass Star ◽  
Dense Cores ◽  
Physical And Chemical

scholarly journals Dense cores in the Seahorse infrared dark cloud: physical properties from modified blackbody fits to the far-infrared–submillimetre spectral energy distributions

2020 ◽  
Vol 644 ◽  
pp. A82
Author(s):  
O. Miettinen
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Initial Conditions ◽  
High Mass ◽  
Spectral Energy ◽  
Mass Star ◽  
Wide Field ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Dense Cores

Context. Infrared dark clouds (IRDCs) can be the birth sites of high-mass stars, and hence determining the physical properties of dense cores in IRDCs is useful to constrain the initial conditions and theoretical models of high-mass star formation. Aims. We aim to determine the physical properties of dense cores in the filamentary Seahorse IRDC G304.74+01.32. Methods. We used data from the Wide-field Infrared Survey Explorer (WISE), Infrared Astronomical Satellite (IRAS), and Herschel in conjuction with our previous 350 and 870 μm observations with the Submillimetre APEX Bolometer Camera (SABOCA) and Large APEX BOlometer CAmera, and constructed the far-IR to submillimetre spectral energy distributions (SEDs) of the cores. The SEDs were fitted using single or two-temperature modified blackbody emission curves to derive the dust temperatures, masses, and luminosities of the cores. Results. For the 12 analysed cores, which include two IR dark cores (no WISE counterpart), nine IR bright cores, and one H II region, the mean dust temperature of the cold (warm) component, the mass, luminosity, H2 number density, and surface density were derived to be 13.3 ± 1.4 K (47.0 ± 5.0 K), 113 ± 29 M⊙, 192 ± 94 L⊙, (4.3 ± 1.2) × 105 cm−3, and 0.77 ± 0.19 g cm−3, respectively. The H II region IRAS 13039-6108a was found to be the most luminous source in our sample ((1.1 ± 0.4) × 103 L⊙). All the cores were found to be gravitationally bound (i.e. the virial parameter αvir < 2). Two out of the nine analysed IR bright cores (22%) were found to follow an accretion luminosity track under the assumptions that the mass accretion rate is 10−5 M⊙ yr−1, the stellar mass is 10% of the parent core mass, and the radius of the central star is 5 R⊙. Most of the remaing ten cores were found to lie within 1 dex below this accretion luminosity track. Seven out of 12 of the analysed cores (58%) were found to lie above the mass-radius thresholds of high-mass star formation proposed in the literature. The surface densities of Σ > 0.4 g cm−3 derived for these seven cores also exceed the corresponding threshold for high-mass star formation. Five of the analysed cores (42%) show evidence of fragmentation into two components in the SABOCA 350 μm image. Conclusions. In addition to the H II region source IRAS 13039-6108a, some of the other cores in Seahorse also appear to be capable of giving birth to high-mass stars. The 22 μm dark core SMM 9 is likely to be the youngest source in our sample that has the potential to form a high-mass star (96 ± 23 M⊙ within a radius of ~0.1 pc). The dense core population in the Seahorse IRDC has comparable average properties to the cores in the well-studied Snake IRDC G11.11-0.12 (e.g. Tdust and L agree within a factor of ~1.8); furthermore, the Seahorse, which lies ~60 pc above the Galactic plane, appears to be a smaller (e.g. three times shorter in projection, ~100 times less massive) version of the Snake. The Seahorse core fragmentation mechanisms appear to be heterogenous, including cases of both thermal and non-thermal Jeans instability. High-resolution follow-up studies are required to address the fragmented cores’ genuine potential of forming high-mass stars.

scholarly journals Rapid and efficient mass collection by a supersonic cloud–cloud collision as a major mechanism of high-mass star formation

2020 ◽  
Author(s):  
Yasuo Fukui ◽  
Tsuyoshi Inoue ◽  
Takahiro Hayakawa ◽  
Kazufumi Torii
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Gravitational Instability ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Major Mechanism ◽  
Dense Cores ◽  
The Magnetic Field

Abstract A supersonic cloud–cloud collision produces a shock-compressed layer which leads to formation of high-mass stars via gravitational instability. We carried out a detailed analysis of the layer by using the numerical simulations of magneto-hydrodynamics which deal with colliding molecular flows at a relative velocity of 20 km s−1 (Inoue & Fukui 2013, ApJ, 774, L31). Maximum density in the layer increases from 1000 cm−3 to more than 105 cm−3 within 0.3 Myr by compression, and the turbulence and the magnetic field in the layer are amplified by a factor of ∼5, increasing the mass accretion rate by two orders of magnitude to more than 10−4 $ M_{\odot } $ yr−1. The layer becomes highly filamentary due to gas flows along the magnetic field lines, and dense cores are formed in the filaments. The massive dense cores have size and mass of 0.03–0.08 pc and 8–$ 50\, M_{\odot } $ and they are usually gravitationally unstable. The mass function of the dense cores is significantly top-heavy as compared with the universal initial mass function, indicating that the cloud–cloud collision preferentially triggers the formation of O and early B stars. We argue that the cloud–cloud collision is a versatile mechanism which creates a variety of stellar clusters from a single O star like RCW 120 and M 20 to tens of O stars of a super star cluster like RCW 38 and a mini-starburst W 43. The core mass function predicted by the present model is consistent with the massive dense cores obtained by recent ALMA observations in RCW 38 (Torii et al. 2021, PASJ, in press) and W 43 (Motte et al. 2018, Nature Astron., 2, 478). Considering the increasing evidence for collision-triggered high-mass star formation, we argue that cloud–cloud collision is a major mechanism of high-mass star formation.

scholarly journals Dense Cores, Filaments, and Outflows in the S255IR Region of High-mass Star Formation

2020 ◽  
Vol 889 (1) ◽  
pp. 43
Author(s):  
Igor I. Zinchenko ◽  
Sheng-Yuan Liu ◽  
Yu-Nung Su ◽  
Kuo-Song Wang ◽  
Yuan Wang
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Mass Star ◽  
Dense Cores

scholarly journals Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

2019 ◽  
Vol 625 ◽  
pp. A134 ◽  
Author(s):  
D. Russeil ◽  
M. Figueira ◽  
A. Zavagno ◽  
F. Motte ◽  
N. Schneider ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
High Mass ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Mass Star ◽  
Massive Star Formation ◽  
Dense Cores

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 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources 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.

scholarly journals Low-Mass Versus High-Mass Star Formation

1997 ◽  
Vol 182 ◽  
pp. 537-549
Author(s):  
T. W. Hartquist ◽  
J. E. Dyson
Keyword(s):  
Star Formation ◽  
Young Stars ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Global Properties ◽  
Low Mass

Structures like the clumps identified in the CO maps of the Rosette Molecular Cloud and the dense cores such as those in B5, a cluster of cores and young low-mass stars, are key to considerations of star formation. Whether star formation is a self-inducing process or one that causes itself to turn off depends greatly on whether the responses of the interclump and intercore media to young stars cause the collapse of clumps or cores to be faster than their ablation. We present a naive introduction to the lengthscales over which such responses are significant, mention ways in which the responses might induce collapse, review some of the little that is known of how flows of media around clumps and cores ablate them, and then return to the issue of the lengthscales over which such responses are significant by considering the global properties of mass-loaded flows in clumpy star forming regions.

scholarly journals MALT90 molecular content on high-mass IR-dark clumps

2018 ◽  
Vol 620 ◽  
pp. A158 ◽  
Author(s):  
Gozde Saral ◽  
Marc Audard ◽  
Yuan Wang
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Chemical Properties ◽  
High Mass ◽  
Mass Star ◽  
Physical And Chemical Properties ◽  
Line Widths ◽  
The Individual ◽  
Physical And Chemical ◽  
And Chemical Properties

Context. High mass stars form in groups or clusters in dense molecular clumps with sizes of 1 pc and masses of 200 M⊙. Infrared-dark clumps and the individual cores within them with sizes < 0.1 pc and masses < 100 M⊙ are important laboratories for high-mass star formation in order to study the initial conditions. Aims. We investigate the physical and chemical properties of high-mass clumps in order to better understand the early evolutionary stages and find targets that show star formation signs such as infall motions or outflows. Methods. We selected the high-mass clumps from ATLASGAL survey that were identified as dark at 8/24 μm wavelengths. We used MALT90 Survey data which provides a molecular line set (HCO+, HNC, HCN, N2H+, H13CO+, HN13C, SiO) to investigate the physical and chemical conditions in early stages of star formation. Results. Eleven sources have significant SiO detection (over 3σ) which usually indicates outflow activity. Thirteen sources are found with blue profiles in both or either HCO+ and/or HNC lines and clump mass infall rates are estimated to be in the range of 0.2 × 10−3 M⊙ yr−1 − 1.8 × 10−2 M⊙ yr−1. The excitation temperature is obtained as < 24 K for all sources. The column densities for optically thin lines of H13CO+ and HN13C are in the range of 0.4–8.8 (×1012) cm−2, and 0.9–11.9 (×1012) cm−2, respectively, while it is in the range of 0.1–7.5 (×1014) cm−2 for HCO+ and HNC lines. The column densities for N2H+ were ranging between 4.4–275.7 (×1012) cm−2 as expected from cold dense regions. Large line widths of N2H+ might indicate turbulence and large line widths of HCO+, HNC, and SiO indicate outflow activities. Mean optical depths are 20.32, and 23.19 for optically thick HCO+ and HCN lines, and 0.39 and 0.45 for their optically thin isotopologues H13CO+ and HN13C, respectively. Conclusions. This study reveals the physical and chemical properties of 30 high-mass IR-dark clumps and the interesting targets among them based on their emission line morphology and kinematics.

scholarly journals Probing fragmentation and velocity sub-structure in the massive NGC 6334 filament with ALMA

2019 ◽  
Vol 632 ◽  
pp. A83 ◽  
Author(s):  
Y. Shimajiri ◽  
Ph. André ◽  
E. Ntormousi ◽  
A. Men’shchikov ◽  
D. Arzoumanian ◽  
...  
Keyword(s):  
Star Formation ◽  
Velocity Structure ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Dense Cores ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Ngc 6334 ◽  
Main Filament

Context. Herschel imaging surveys of galactic interstellar clouds support a paradigm for low-mass star formation in which dense molecular filaments play a crucial role. The detailed fragmentation properties of star-forming filaments remain poorly understood, however, and the validity of the filament paradigm in the intermediate- to high-mass regime is still unclear. Aims. Here, following up on an earlier 350 μm dust continuum study with the ArTéMiS camera on the APEX telescope, we investigate the detailed density and velocity structure of the main filament in the high-mass star-forming region NGC 6334. Methods. We conducted ALMA Band 3 observations in the 3.1 mm continuum and of the N2H+(1–0), HC5N(36–35), HNC(1–0), HC3N(10–9), CH3CCH(6–5), and H2CS(3–2) lines at an angular resolution of ~3′′, corresponding to 0.025 pc at a distance of 1.7 kpc. Results. The NGC 6334 filament was detected in both the 3.1 mm continuum and the N2H+, HC3N, HC5N, CH3CCH, and H2CS lines with ALMA. We identified twenty-six compact (<0.03 pc) dense cores at 3.1 mm and five velocity-coherent fiber-like features in N2H+ within the main filament. The typical length (~0.5 pc) of, and velocity difference (~0.8 km s−1) between, the fiber-like features of the NGC 6334 filament are reminiscent of the properties for the fibers of the low-mass star-forming filament B211/B213 in the Taurus cloud. Only two or three of the five velocity-coherent features are well aligned with the NGC 6334 filament and may represent genuine, fiber sub-structures; the other two features may trace accretion flows onto the main filament. The mass distribution of the ALMA 3.1 mm continuum cores has a peak at ~10 M⊙, which is an order of magnitude higher than the peak of the prestellar core mass function in nearby, low-mass star-forming clouds. The cores can be divided into seven groups, closely associated with dense clumps seen in the ArTéMiS 350 μm data. The projected separation between ALMA dense cores (0.03–0.1 pc) and the projected spacing between ArTéMiS clumps (0.2–0.3 pc) are roughly consistent with the effective Jeans length (0.08 ± 0.03 pc) in the filament and a physical scale of about four times the filament width, respectively, if the inclination angle of the filament to line of sight is ~30°. These two distinct separation scales are suggestive of a bimodal fragmentation process in the filament. Conclusions. Despite being one order of magnitude denser and more massive than the Taurus B211/B213 filament, the NGC 6334 filament has a density and velocity structure that is qualitatively very similar. The main difference is that the dense cores embedded in the NGC 6334 filament appear to be an order of magnitude denser and more massive than the cores in the Taurus filament. This suggests that dense molecular filaments may evolve and fragment in a similar manner in low- and high-mass star-forming regions, and that the filament paradigm may hold in the intermediate-mass (if not high-mass) star formation regime.

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