Magnetic fields at the onset of high-mass star formation

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

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa079 ◽

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.

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Measuring Magnetic Fields from Water Masers Associated with a Synchrotron Protostellar Jet

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318000017 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 215-218

Author(s):

Ciriaco Goddi ◽

Gabriele Surcis

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Zeeman Splitting ◽

High Mass ◽

Local Magnetic Field ◽

Mass Star ◽

Dominant Component ◽

Field Lines ◽

Water Masers ◽

The Magnetic Field

AbstractThe Turner-Welch Object in the W3(OH) high-mass star forming complex drives a synchrotron jet, which is quite exceptional for a high-mass protostar, and is associated with a strongly polarized water maser source, W3(H2O), making it an optimal target to investigate the role of magnetic fields on the innermost scales of protostellar disk-jet systems. We report here full polarimetric VLBA observations of water masers. The linearly polarized emission from water masers provides clues on the orientation of the local magnetic field, while the measurement of the Zeeman splitting from circular polarization provides its strength. By combining the information on the measured orientation and strength of the magnetic field with the knowledge of the maser velocities, we infer that the magnetic field evolves from having a dominant component parallel to the outflow velocity in the pre-shock gas (with field strengths of the order of a few tens of mG), to being mainly dominated by the perpendicular component (of order of a few hundred of mG) in the post-shock gas where the water masers are excited. The general implication is that in the undisturbed (i.e. not-shocked) circumstellar gas, the flow velocities would follow closely the magnetic field lines, while in the shocked gas the magnetic field would be re-configured to be parallel to the shock front as a consequence of gas compression.

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Magnetic massive stars in star forming regions

Proceedings of the International Astronomical Union ◽

10.1017/s174392131900382x ◽

2018 ◽

Vol 14 (A30) ◽

pp. 132-132

Author(s):

Swetlana Hubrig ◽

Markus Schöller ◽

Silva P. Järvinen

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Active Sites ◽

Massive Stars ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Gas Cloud

AbstractOne idea for the origin of magnetic fields in massive stars suggests that the magnetic field is the fossil remnant of the Galactic ISM magnetic field, amplified during the collapse of the magnetised gas cloud. A search for the presence of magnetic fields in massive stars located in active sites of star formation led to the detection of rather strong magnetic fields in a few young stars. Future spectropolarimetric observations are urgently needed to obtain insights into the mechanisms that drive the generation of kG magnetic fields during high-mass star formation.

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Magnetic Fields in Massive Star-forming Regions (MagMaR). II. Tomography through Dust and Molecular Line Polarization in NGC 6334I(N)

The Astrophysical Journal ◽

10.3847/1538-4357/ac28a1 ◽

2021 ◽

Vol 923 (2) ◽

pp. 204

Author(s):

Paulo C. Cortés ◽

Patricio Sanhueza ◽

Martin Houde ◽

Sergio Martín ◽

Charles L. H. Hull ◽

...

Keyword(s):

Magnetic Field ◽

Dust Emission ◽

High Mass ◽

Dispersion Function ◽

Mass Star ◽

Length Scales ◽

Star Forming ◽

Multiple Length Scales ◽

Polarized Emission ◽

The Magnetic Field

Abstract Here, we report ALMA detections of polarized emission from dust, CS(J = 5 → 4), and C33S(J = 5 → 4) toward the high-mass star-forming region NGC 6334I(N). A clear “hourglass” magnetic field morphology was inferred from the polarized dust emission, which is also directly seen from the polarized CS emission across velocity, where the polarization appears to be parallel to the field. By considering previous findings, the field retains a pinched shape that can be traced to clump length scales from the envelope scales traced by ALMA, suggesting that the field is dynamically important across multiple length scales in this region. The CS total intensity emission is found to be optically thick (τ CS = 32 ± 12) while the C33S emission appears to be optically thin ( τ C 33 S = 0.1 ± 0.01 ). This suggests that sources of anisotropy other than large velocity gradients, i.e., anisotropies in the radiation field, are required to explain the polarized emission from CS seen by ALMA. By using four variants of the Davis–Chandrasekhar–Fermi technique and the angle dispersion function methods (ADF), we obtain an average of the estimates for the magnetic field strength on the plane of the sky of B pos = 16 mG from the dust and B pos ∼ 2 mG from the CS emission, where each emission traces different molecular hydrogen number densities. This effectively enables a tomographic view of the magnetic field within a single ALMA observation.

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Gravity and Rotation Drag the Magnetic Field in High-mass Star Formation

The Astrophysical Journal ◽

10.3847/1538-4357/abc019 ◽

2020 ◽

Vol 904 (2) ◽

pp. 168

Author(s):

Henrik Beuther ◽

Juan D. Soler ◽

Hendrik Linz ◽

Thomas Henning ◽

Caroline Gieser ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

High Mass ◽

Mass Star ◽

The Magnetic Field

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MAGMO: Mapping the Galactic Magnetic field through OH masers

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314011715 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 402-402 ◽

Cited By ~ 1

Author(s):

James A. Green ◽

Naomi M. McClure-Griffiths ◽

James L. Caswell ◽

Tim Robishaw ◽

Lisa Harvey-Smith ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Ground State ◽

Large Scale ◽

Zeeman Splitting ◽

High Mass ◽

Mass Star ◽

Galactic Magnetic Field ◽

Maser Emission

AbstractWe are undertaking a project (MAGMO) to examine large-scale magnetic fields pervading regions of high-mass star formation. The project will test if the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities encountered in high-mass star forming regions. This will be achieved through correlating targeted observations of ground-state hydroxyl (OH) maser emission towards hundreds of sites of high-mass star formation spread throughout the spiral arms of the Milky Way. Through the Zeeman splitting of the OH maser emission these observations will determine the strength and orientation of the in-situ magnetic field. The completion of the southern hemisphere Methanol Multibeam survey has provided an abundance of targets for ground-state OH maser observations, approximately 1000 sites of high-mass star formation. With this sample, much larger and more homogeneous than previously available, we will have the statistics necessary to outweigh random fluctuations and observe an underlying Galactic magnetic field if it exists. We presented details of the overall progress of the project illustrated by the results of a pilot sample of sources towards the Carina-Sagittarius spiral arm tangent, where a coherent field is implied.

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Submillimeter Array Observations of Magnetic Fields in Star Forming Regions

Proceedings of the International Astronomical Union ◽

10.1017/s174392131100024x ◽

2010 ◽

Vol 6 (S270) ◽

pp. 103-106

Author(s):

R. Rao ◽

J.-M. Girart ◽

D. P. Marrone

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Computational Models ◽

Dominant Role ◽

Theoretical Models ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Low Mass

AbstractThere have been a number of theoretical and computational models which state that magnetic fields play an important role in the process of star formation. Competing theories instead postulate that it is turbulence which is dominant and magnetic fields are weak. The recent installation of a polarimetry system at the Submillimeter Array (SMA) has enabled us to conduct observations that could potentially distinguish between the two theories. Some of the nearby low mass star forming regions show hour-glass shaped magnetic field structures that are consistent with theoretical models in which the magnetic field plays a dominant role. However, there are other similar regions where no significant polarization is detected. Future polarimetry observations made by the Submillimeter Array should be able to increase the sample of observed regions. These measurements will allow us to address observationally the important question of the role of magnetic fields and/or turbulence in the process of star formation.

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ALMA resolves the hourglass magnetic field in G31.41+0.31

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935701 ◽

2019 ◽

Vol 630 ◽

pp. A54 ◽

Cited By ~ 8

Author(s):

M. T. Beltrán ◽

M. Padovani ◽

J. M. Girart ◽

D. Galli ◽

R. Cesaroni ◽

...

Keyword(s):

Magnetic Field ◽

Velocity Gradient ◽

Flux Ratio ◽

High Mass ◽

Continuum Emission ◽

Mass Star ◽

Star Forming ◽

The Core ◽

Molecular Core ◽

The Magnetic Field

Context. Submillimeter Array (SMA) 870 μm polarization observations of the hot molecular core G31.41+0.31 revealed one of the clearest examples up to date of an hourglass-shaped magnetic field morphology in a high-mass star-forming region. Aims. To better establish the role that the magnetic field plays in the collapse of G31.41+0.31, we carried out Atacama Large Millimeter/ submillimeter Array (ALMA) observations of the polarized dust continuum emission at 1.3 mm with an angular resolution four times higher than that of the previous (sub)millimeter observations to achieve an unprecedented image of the magnetic field morphology. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6). The resulting synthesized beam is 0′′.28×0′′.20 which, at the distance of the source, corresponds to a spatial resolution of ~875 au. Results. The observations resolve the structure of the magnetic field in G31.41+0.31 and allow us to study the field in detail. The polarized emission in the Main core of G31.41+0.41is successfully fit with a semi-analytical magnetostatic model of a toroid supported by magnetic fields. The best fit model suggests that the magnetic field is well represented by a poloidal field with a possible contribution of a toroidal component of ~10% of the poloidal component, oriented southeast to northwest at approximately −44° and with an inclination of approximately −45°. The magnetic field is oriented perpendicular to the northeast to southwest velocity gradient detected in this core on scales from 103 to 104 au. This supports the hypothesis that the velocity gradient is due to rotation of the core and suggests that such a rotation has little effect on the magnetic field. The strength of the magnetic field estimated in the central region of the core with the Davis–Chandrasekhar-Fermi method is ~8–13 mG and implies that the mass-to-flux ratio in this region is slightly supercritical. Conclusions. The magnetic field in G31.41+0.31 maintains an hourglass-shaped morphology down to scales of <1000 au. Despite the magnetic field being important in G31.41+0.31, it is not enough to prevent fragmentation and collapse of the core, as demonstrated by the presence of at least four sources embedded in the center of the core.

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