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

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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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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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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ALMA reveals the magnetic field evolution in the high-mass star forming complex G9.62+0.19

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834100 ◽

2019 ◽

Vol 626 ◽

pp. A36 ◽

Cited By ~ 6

Author(s):

D. Dall’Olio ◽

W. H. T. Vlemmings ◽

M. V. Persson ◽

F. O. Alves ◽

H. Beuther ◽

...

Keyword(s):

Magnetic Field ◽

Field Strength ◽

Magnetic Field Strength ◽

High Mass ◽

Mass Star ◽

Evolutionary Sequence ◽

Star Forming ◽

High Magnetic Field Strength ◽

The Magnetic Field ◽

Linear Polarisation

Context. The role of magnetic fields during the formation of high-mass stars is not yet fully understood, and the processes related to the early fragmentation and collapse are as yet largely unexplored. The high-mass star forming region G9.62+0.19 is a well known source, presenting several cores at different evolutionary stages. Aims. We seek to investigate the magnetic field properties at the initial stages of massive star formation. We aim to determine the magnetic field morphology and strength in the high-mass star forming region G9.62+0.19 to investigate its relation to the evolutionary sequence of the cores. Methods. We made use of Atacama Large Millimeter Array (ALMA) observations in full polarisation mode at 1 mm wavelength (Band 7) and we analysed the polarised dust emission. We estimated the magnetic field strength via the Davis–Chandrasekhar–Fermi and structure function methods. Results. We resolve several protostellar cores embedded in a bright and dusty filamentary structure. The polarised emission is clearly detected in six regions: two in the northern field and four in the southern field. Moreover the magnetic field is orientated along the filament and appears perpendicular to the direction of the outflows. The polarisation vectors present ordered patterns and the cores showing polarised emission are less fragmented. We suggest an evolutionary sequence of the magnetic field, and the less evolved hot core exhibits a stronger magnetic field than the more evolved hot core. An average magnetic field strength of the order of 11 mG was derived, from which we obtain a low turbulent-to-magnetic energy ratio, indicating that turbulence does not significantly contribute to the stability of the clump. We report a detection of linear polarisation from thermal line emission, probably from methanol or carbon dioxide, and we tentatively compared linear polarisation vectors from our observations with previous linearly polarised OH masers observations. We also compute the spectral index, column density, and mass for some of the cores. Conclusions. The high magnetic field strength and smooth polarised emission indicate that the magnetic field could play an important role in the fragmentation and the collapse process in the star forming region G9.62+019 and that the evolution of the cores can be magnetically regulated. One core shows a very peculiar pattern in the polarisation vectors, which can indicate a compressed magnetic field. On average, the magnetic field derived by the linear polarised emission from dust, thermal lines, and masers is pointing in the same direction and has consistent strength.

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Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038024 ◽

2020 ◽

Vol 640 ◽

pp. A111

Author(s):

C. Arce-Tord ◽

F. Louvet ◽

P. C. Cortes ◽

F. Motte ◽

C. L. H. Hull ◽

...

Keyword(s):

Magnetic Field ◽

High Mass ◽

Continuum Emission ◽

High Angular Resolution ◽

Mass Star ◽

Star Forming ◽

The Core ◽

Dense Cores ◽

The Impact ◽

The Magnetic Field

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region. Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of ~2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission. Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20–50° with respect to the magnetic field. As for the outflows, they could be oriented 50–70° with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions. Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20–50° preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

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Dust polarized emission observations of NGC 6334. BISTRO reveals the details of the complex but organized magnetic field structure of the high-mass star-forming hub-filament network

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038624 ◽

2021 ◽

Author(s):

D. Arzoumanian ◽

R. Furuya ◽

T. Hasegawa ◽

M. Tahani ◽

S. Sadavoy ◽

...

Keyword(s):

Magnetic Field ◽

Field Structure ◽

High Mass ◽

Mass Star ◽

Magnetic Field Structure ◽

Star Forming ◽

Polarized Emission ◽

Ngc 6334 ◽

Filament Network

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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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High resolution magnetic field measurements in high-mass star-forming regions using masers

10.22323/1.178.0034 ◽

2016 ◽

Author(s):

Gabriele Surcis ◽

Wouter H.T. Vlemmings ◽

Huib Jan van Langevelde ◽

Busaba Hutawarakorn Kramer

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Field Measurements ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Magnetic Field Measurements

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Methanol masers and magnetic field in IRAS18089-1732

Proceedings of the International Astronomical Union ◽

10.1017/s174392131701016x ◽

2017 ◽

Vol 13 (S336) ◽

pp. 285-286

Author(s):

Daria Dall’Olio ◽

W. H. T. Vlemmings ◽

G. Surcis ◽

H. Beuther ◽

B. Lankhaar ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

High Mass ◽

Small Scale ◽

Star Forming ◽

Large Scale Field ◽

The Impact ◽

Theoretical Simulations ◽

The Magnetic Field

AbstractTheoretical simulations have shown that magnetic fields play an important role in massive star formation: they can suppress fragmentation in the star forming cloud, enhance accretion via disc and regulate outflows and jets. However, models require specific magnetic configurations and need more observational constraints to properly test the impact of magnetic fields. We investigate the magnetic field structure of the massive protostar IRAS18089-1732, analysing 6.7 GHz CH3OH maser MERLIN observations. IRAS18089-1732 is a well studied high mass protostar, showing a hot core chemistry, an accretion disc and a bipolar outflow. An ordered magnetic field oriented around its disc has been detected from previous observations of polarised dust. This gives us the chance to investigate how the magnetic field at the small scale probed by masers relates to the large scale field probed by the dust.

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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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