Zeeman splitting of OH masers and the galactic magnetic field

Zeeman measurements of OH masers are used to probe the magnetic field around regions of massive star formation. Previous observations suggested that OH maser field directions were aligned in a clockwise sense in the Milky Way, but recent data from a large-scale VLA survey do not support this hypothesis. However, these observations suggest that the magnetic field of the Milky Way is correlated on kiloparsec scales.

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A MERLIN study of 6 GHz excited OH & 6.7 GHz methanol masers in ON1

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307012938 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 188-189

Author(s):

James A. Green ◽

A. M. S. Richards ◽

H. Flood ◽

W. H. T. Vlemmings ◽

R. J. Cohen

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Cross Correlation ◽

Massive Star ◽

Zeeman Splitting ◽

Massive Star Formation ◽

Star Formation Region ◽

Formation Region ◽

Methanol Masers ◽

Field Strengths

AbstractMERLIN observations of 6.668-GHz Methanol and 6.035-GHz OH emission from the known massive star-formation region ON1 are presented. Maser components are found to lie at the southern edge of the UCHII with consistent polarization angles across the strongest features. Zeeman splitting of OH shows magnetic field strengths between +0.4 to −5.3 mG and from cross-correlation a tentative methanol magnetic field of −18mG is detected.

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8.14. Magnetic fields in star-forming regions of our Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900085272 ◽

1998 ◽

Vol 184 ◽

pp. 371-372

Author(s):

B. Hutawarakorn ◽

R. J. Cohen

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Zeeman Splitting ◽

Theoretical Work ◽

Field Configuration ◽

Galactic Magnetic Field ◽

Star Forming ◽

Star Forming Regions ◽

The Magnetic Field

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.

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A survey of molecular cores in M 17 SWex

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz061 ◽

2019 ◽

Cited By ~ 2

Author(s):

Tomomi Shimoikura ◽

Kazuhito Dobashi ◽

Asha Hirose ◽

Fumitaka Nakamura ◽

Yoshito Shimajiri ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Massive Star ◽

Near Infrared ◽

Young Stellar Objects ◽

High Mass ◽

Physical Parameters ◽

Massive Star Formation ◽

Dark Cloud ◽

The Magnetic Field

Abstract A survey of molecular cores covering the infrared dark cloud known as the M 17 southwest extension (M 17 SWex) has been carried out with the 45 m Nobeyama Radio Telescope. Based on the N2H+ (J = 1–0) data obtained, we have identified 46 individual cores whose masses are in the range from 43 to $3026\, {M}_{\odot }$. We examined the relationship between the physical parameters of the cores and those of young stellar objects (YSOs) associated with the cores found in the literature. The comparison of the virial mass and the core mass indicates that most of the cores can be gravitationally stable if we assume a large external pressure. Among the 46 cores, we found four massive cores with YSOs. They have large masses of $\gtrsim 1000\, M_{\odot }$ and line widths of $\gtrsim 2.5\:$km s−1 which are similar to those of clumps forming high-mass stars. However, previous studies have shown that there is no active massive star formation in this region. Recent measurements of near-infrared polarization imply that the magnetic field around M 17 SWex is likely to be strong enough to support the cores against self-gravity. We therefore suggest that the magnetic field may prevent the cores from collapsing, causing the low level of massive star formation in M 17 SWex.

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OH masers and magnetic fields in massive star-forming regions: ON1

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307002402 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 452-452

Author(s):

S. Nammahachak ◽

K. Asanok ◽

B. Hutawarakorn Kramer ◽

R. J. Cohen ◽

O. Muanwong ◽

...

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Massive Star ◽

Zeeman Splitting ◽

Young Stars ◽

Star Forming ◽

Physical Conditions ◽

Bipolar Outflow ◽

Star Forming Regions ◽

The Magnetic Field

AbstractOH masers are sensitive probes of the kinematics and physical conditions, and give unique information on the magnetic field through their polarization. Zeeman splitting of the OH lines can give the magnetic field strength and direction. Observing OH masers with MERLIN we studied the bipolar outflow in the star-forming region ON1, which hosts one of the earliest known ultra-compact (UC) HII regions. The strongest masers lie near the southern edge of the UCHII region in an elongated distribution. The maser distribution is orthogonal to the bipolar outflow seen in HCO+, suggesting that the OH masers may be embedded in a molecular disk or torus around a young B0.3 star, most likely tracing a shock front. An isolated group of 1720-MHz masers is also seen to the East. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from -0.4 to -4.6 mG. These results add to the growing body of evidence for OH masers associated with molecular disks or tori at the centre of bipolar outflow from massive young stars, and for a significant role played by the magnetic field in generating or channeling the bipolar outflow. Further details are presented by Nammahachak et al. 2006.

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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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Observation of triggering in the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001494 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 212-216 ◽

Cited By ~ 1

Author(s):

L. Deharveng ◽

A. Zavagno ◽

B. Lefloch ◽

J. Caplan ◽

M. Pomarès

Keyword(s):

Star Formation ◽

Massive Star ◽

Milky Way ◽

Turbulent Medium ◽

Massive Star Formation ◽

Collapse Process

AbstractWe show how the expansion of classical Galactic Hiiregions can trigger massive-star formation via the collect & collapse process. We give examples of this process at work. We suggest that it also works in a turbulent medium.

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The Magnetic Field Near the Local Bubble

International Astronomical Union Colloquium ◽

10.1017/s0252921100071037 ◽

1997 ◽

Vol 166 ◽

pp. 227-238

Author(s):

Carl Heiles

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Zeeman Splitting ◽

Relativistic Electrons ◽

Local Bubble ◽

Scale Field ◽

Large Scale Field ◽

Field Lines ◽

Hi Shells ◽

The Magnetic Field

AbstractThere are almost no direct observational indicators of the magnetic field inside the local bubble. Just outside the bubble, the best tracers are stellar polarization and HI Zeeman splitting. These show that the local field does not follow the large-scale Galactic field. Here we discuss whether the deformation of the large-scale field by the local HI shells is consistent with the observations. We concentrate on the Loop 1 region, and find that the field lines are well-explained by this idea; in addition, the bright radio filaments of Radio Loop 1 delineate particular field lines that are “lit up” by an excess of relativistic electrons.

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Magnetic field evolution in dwarf and Magellanic-type galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730566 ◽

2018 ◽

Vol 611 ◽

pp. A7 ◽

Cited By ~ 1

Author(s):

H. Siejkowski ◽

M. Soida ◽

K. T. Chyży

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Large Scale ◽

Magnetic Energy ◽

Galactic Disk ◽

Cosmic Ray ◽

Dark Matter Halo ◽

Field Evolution ◽

Low Mass ◽

The Magnetic Field

Aims. Low-mass galaxies radio observations show in many cases surprisingly high levels of magnetic field. The mass and kinematics of such objects do not favour the development of effective large-scale dynamo action. We attempted to check if the cosmic-ray-driven dynamo can be responsible for measured magnetization in this class of poorly investigated objects. We investigated how starburst events on the whole, as well as when part of the galactic disk, influence the magnetic field evolution. Methods. We created a model of a dwarf/Magellanic-type galaxy described by gravitational potential constituted from two components: the stars and the dark-matter halo. The model is evolved by solving a three-dimensional (3D) magnetohydrodynamic equation with an additional cosmic-ray component, which is approximated as a fluid. The turbulence is generated in the system via supernova explosions manifested by the injection of cosmic-rays. Results. The cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field even in low-mass dwarf/Magellanic-type galaxies. The e-folding times of magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km s−1) and fast (100 km s−1) rotators, respectively. The amplification is being suppressed as the system reaches the equipartition level between kinetic, magnetic, and cosmic-ray energies. An episode of star formation burst amplifies the magnetic field but only for a short time while increased star formation activity holds. We find that a substantial amount of gas is expelled from the galactic disk, and that the starburst events increase the efficiency of this process.

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The Massive Star Population at the Center of the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314007315 ◽

2014 ◽

Vol 9 (S307) ◽

pp. 426-430

Author(s):

Francisco Najarro ◽

Diego de la Fuente ◽

Tom R. Geballe ◽

Don F. Figer ◽

D. John Hillier

Keyword(s):

Star Formation ◽

Infrared Spectra ◽

Massive Star ◽

Milky Way ◽

Galactic Center ◽

Massive Stars ◽

Harsh Environment ◽

Massive Star Formation ◽

Tidal Interactions ◽

Stellar Properties

AbstractRecent detection of a large number of apparently isolated massive stars within the inner 80 pc of the Galactic Center has raised fundamental questions regarding massive star formation in a such a dense and harsh environment. Are these isolated stars the results of tidal interactions between clusters, are they escapees from a disrupted cluster, or do they represent a new mode of massive star formation in isolation? Noting that most of the isolated massive stars have spectral analogs in the Quintuplet Cluster, we have undertaken a combined analysis of the infrared spectra of both selected Quintuplet stars and the isolated objects using Gemini North spectroscopy. We present preliminary results, aiming at α-elements vs iron abundances, stellar properties, ages and radial velocities which will differentiate the top-heavy and star-formation scenarios.

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