EVOLUTION OF MAGNETIC FIELDS IN HIGH MASS STAR FORMATION: SUBMILLIMETER ARRAY DUST POLARIZATION IMAGE OF THE ULTRACOMPACT H II REGION G5.89–0.39

Abstract We report on a study of the high-mass star formation in the H ii region W 28 A2 by investigating the molecular clouds that extend over ∼5–10 pc from the exciting stars using the 12CO and 13CO (J = 1–0) and 12CO (J = 2–1) data taken by NANTEN2 and Mopra observations. These molecular clouds consist of three velocity components with CO intensity peaks at VLSR ∼ −4 km s−1, 9 km s−1, and 16 km s−1. The highest CO intensity is detected at VLSR ∼ 9 km s−1, where the high-mass stars with spectral types O6.5–B0.5 are embedded. We found bridging features connecting these clouds toward the directions of the exciting sources. Comparisons of the gas distributions with the radio continuum emission and 8 μm infrared emission show spatial coincidence/anti-coincidence, suggesting physical associations between the gas and the exciting sources. The 12CO J = 2–1 to 1–0 intensity ratio shows a high value (≳0.8) toward the exciting sources for the −4 km s−1 and +9 km s−1 clouds, possibly due to heating by the high-mass stars, whereas the intensity ratio at the CO intensity peak (VLSR ∼ 9 km s−1) decreases to ∼0.6, suggesting self absorption by the dense gas in the near side of the +9 km s−1 cloud. We found partly complementary gas distributions between the −4 km s−1 and +9 km s−1 clouds, and the −4 km s−1 and +16 km s−1 clouds. The exciting sources are located toward the overlapping region in the −4 km s−1 and +9 km s−1 clouds. Similar gas properties are found in the Galactic massive star clusters RCW 38 and NGC 6334, where an early stage of cloud collision to trigger the star formation is suggested. Based on these results, we discuss the possibility of the formation of high-mass stars in the W 28 A2 region being triggered by cloud–cloud collision.

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FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VIII. Possible evidence of cloud–cloud collisions triggering high-mass star formation in the giant molecular cloud M 16 (Eagle Nebula)

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa083 ◽

2020 ◽

Author(s):

Atsushi Nishimura ◽

Shinji Fujita ◽

Mikito Kohno ◽

Daichi Tsutsumi ◽

Tetsuhiro Minamidani ◽

...

Keyword(s):

Star Formation ◽

Molecular Cloud ◽

Velocity Structure ◽

Galactic Plane ◽

High Mass ◽

Mass Star ◽

Collision Event ◽

Giant Molecular Cloud ◽

Eagle Nebula ◽

H Ii Region

Abstract M 16, the Eagle Nebula, is an outstanding H ii region which exhibits extensive high-mass star formation and hosts remarkable “pillars.” We herein obtained new 12COJ = 1–0 data for the region observed with NANTEN2, which were combined with the 12COJ = 1–0 data obtained using the FOREST unbiased galactic plane imaging with Nobeyama 45 m telescope (FUGIN) survey. These observations revealed that a giant molecular cloud (GMC) of ∼1.3 × 105 M⊙ is associated with M 16, which extends for 30 pc perpendicularly to the galactic plane, at a distance of 1.8 kpc. This GMC can be divided into the northern (N) cloud, the eastern (E) filament, the southeastern (SE) cloud, the southeastern (SE) filament, and the southern (S) cloud. We also found two velocity components (blueshifted and redshifted components) in the N cloud. The blueshifted component shows a ring-like structure, and the redshifted one coincides with the intensity depression of the ring-like structure. The position–velocity diagram of the components showed a V-shaped velocity feature. The spatial and velocity structures of the cloud indicated that two different velocity components collided with each other at a relative velocity of 11.6 km s−1. The timescale of the collision was estimated to be ∼4 × 105 yr. The collision event reasonably explains the formation of the O9V star ALS 15348, as well as the shape of the Spitzer bubble N19. A similar velocity structure was found in the SE cloud, which is associated with the O7.5V star HD 168504. In addition, the complementary distributions of the two velocity components found in the entire GMC suggested that the collision event occurred globally. On the basis of the above results, we herein propose a hypothesis that the collision between the two components occurred sequentially over the last several 106 yr and triggered the formation of O-type stars in the NGC 6611 cluster in M 16.

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Magnetic fields at the onset of high-mass star formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732378 ◽

2018 ◽

Vol 614 ◽

pp. A64 ◽

Cited By ~ 12

Author(s):

H. Beuther ◽

J. D. Soler ◽

W. Vlemmings ◽

H. Linz ◽

Th. Henning ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Spectral Line ◽

Function Analysis ◽

High Mass ◽

Mass Star ◽

Starting Point ◽

Polarized Emission ◽

The Magnetic Field

Context. The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims. We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods. The Atacama Large Millimeter Array is used at 1.3 mm wavelength in full polarization mode to study the polarized emission, and, using this, the magnetic field morphologies and strengths of the high-mass starless region IRDC 18310-4. Results. Polarized emission is clearly detected in four sub-cores of the region; in general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.3–5.3 mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 – depending on column density – indicates that the region starts to collapse, which is consistent with the previous spectral line analysis of the region. Conclusions. While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.

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A new probe of magnetic fields during high-mass star formation

Astronomy and Astrophysics ◽

10.1051/0004-6361:200809447 ◽

2008 ◽

Vol 484 (3) ◽

pp. 773-781 ◽

Cited By ~ 46

Author(s):

W. H. T. Vlemmings

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

High Mass ◽

Mass Star

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THE INTERPLAY OF MAGNETIC FIELDS, FRAGMENTATION, AND IONIZATION FEEDBACK IN HIGH-MASS STAR FORMATION

The Astrophysical Journal ◽

10.1088/0004-637x/729/1/72 ◽

2011 ◽

Vol 729 (1) ◽

pp. 72 ◽

Cited By ~ 148

Author(s):

Thomas Peters ◽

Robi Banerjee ◽

Ralf S. Klessen ◽

Mordecai-Mark Mac Low

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

High Mass ◽

Mass Star

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The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IV. Star Formation Signatures in G023.477

The Astrophysical Journal ◽

10.3847/1538-4357/ac2365 ◽

2021 ◽

Vol 923 (2) ◽

pp. 147

Author(s):

Kaho Morii ◽

Patricio Sanhueza ◽

Fumitaka Nakamura ◽

James M. Jackson ◽

Shanghuo Li ◽

...

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Line Emission ◽

High Mass ◽

Mass Star ◽

Dark Cloud ◽

Early Stages ◽

Star Formation Activity ◽

Prestellar Cores ◽

The Masses

Abstract With a mass of ∼1000 M ⊙ and a surface density of ∼0.5 g cm−2, G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μm Dark High-mass Clumps in Early Stages. We have conducted ∼1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M ⊙. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2CO and CH3OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8–19 M ⊙). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.

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High-mass star formation in Orion B triggered by cloud–cloud collision: Merging molecular clouds in NGC 2024

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa049 ◽

2020 ◽

Cited By ~ 2

Author(s):

Rei Enokiya ◽

Akio Ohama ◽

Rin Yamada ◽

Hidetoshi Sano ◽

Shinji Fujita ◽

...

Keyword(s):

Star Formation ◽

Angular Resolution ◽

Close Correlation ◽

High Mass ◽

Mass Star ◽

B Stars ◽

Star Forming ◽

Complementary Distribution ◽

H Ii Region ◽

High Column

Abstract We performed new comprehensive 13CO(J = 2–1) observations toward NGC 2024, the most active star-forming region in Orion B, with an angular resolution of ∼100″ obtained with Nanten2. We found that the associated cloud consists of two independent velocity components. The components are physically connected to the H ii region as evidenced by their close correlation with the dark lanes and the emission nebulosity. The two components show complementary distribution with a displacement of ∼0.6 pc. Such complementary distribution is typical to colliding clouds discovered in regions of high-mass star formation. We hypothesize that a cloud–cloud collision between the two components triggered the formation of the late O-type stars and early B stars localized within 0.3 pc of the cloud peak. The duration time of the collision is estimated to be 0.3 million years from a ratio of the displacement and the relative velocity ∼3 km s−1 corrected for probable projection. The high column density of the colliding cloud ∼1023 cm−2 is similar to those in the other high-mass star clusters in RCW 38, Westerlund 2, NGC 3603, and M 42, which are likely formed under trigger by cloud–cloud collision. The present results provide an additional piece of evidence favorable to high-mass star formation by a major cloud–cloud collision in Orion.

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Revealing magnetic fields towards massive protostars: a multi-scale approach using masers and dust

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003661 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 111-112

Author(s):

Daria Dall’Olio ◽

W. H. T. Vlemmings ◽

M. V. Persson

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Spatial Scales ◽

High Mass ◽

Small Scale ◽

Evolutionary Stage ◽

Mass Star ◽

Filamentary Structure ◽

The Magnetic Field

AbstractMagnetic fields play a significant role during star formation processes, hindering the fragmentation and the collapse of the parental cloud, and affecting the accretion mechanisms and feedback phenomena. However, several questions still need to be addressed to clarify the importance of magnetic fields at the onset of high-mass star formation, such as how strong they are and at what evolutionary stage and spatial scales their action becomes relevant. Furthermore, the magnetic field parameters are still poorly constrained especially at small scales, i.e. few astronomical units from the central object, where the accretion disc and the base of the outflow are located. Thus we need to probe magnetic fields at different scales, at different evolutionary steps and possibly with different tracers. We show that the magnetic field morphology around high-mass protostars can be successfully traced at different scales by observing maser and dust polarised emission. A confirmation that they are effective tools is indeed provided by our recent results from 6.7 GHz MERLIN observations of the massive protostar IRAS 18089-1732, where we find that the small-scale magnetic field probed by methanol masers is consistent with the large-scale magnetic field probed by dust (Dall’Olio et al. 2017 A&A 607, A111). Moreover we present results obtained from our ALMA Band 7 polarisation observations of G9.62+0.20, which is a massive star-forming region with a sequence of cores at different evolutionary stages (Dall’Olio et al. submitted to A&A). In this region we resolve several protostellar cores embedded in a bright and dusty filamentary structure. The magnetic field morphology and strength in different cores is related to the evolutionary sequence of the star formation process which is occurring across the filament.

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