scholarly journals The magnetic field in luminous star-forming galaxies

2008 ◽  
Vol 4 (S259) ◽  
pp. 493-498
Author(s):  
Timothy Robishaw ◽  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Emission Line ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Star Forming ◽  
The Magnetic Field

AbstractAn ongoing search for Zeeman splitting in the 1667 MHz OH megamaser emission from luminous star-forming galaxies has yielded numerous detections. These results, in addition to being the first extragalactic measurement of the Zeeman effect in an emission line, suggest that OH megamasers are excellent extragalactic magnetometers. We review the progress of our survey and discuss future observations.

scholarly journals The magnetic field in the dense photodissociation region of DR 21

2020 ◽  
Author(s):  
Atanu Koley ◽  
Nirupam Roy ◽  
Karl M Menten ◽  
Arshia M Jacob ◽  
Thushara G S Pillai ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Weak Field ◽  
Field Energy ◽  
Evolutionary Stage ◽  
Maser Emission ◽  
The Magnetic Field ◽  
Photodissociation Region

Abstract Measuring interstellar magnetic fields is extremely important for understanding their role in different evolutionary stages of interstellar clouds and of star formation. However, detecting the weak field is observationally challenging. We present measurements of the Zeeman effect in the 1665 and 1667 MHz (18 cm) lines of the hydroxyl radical (OH) lines toward the dense photodissociation region (PDR) associated with the compact H ii region DR 21 (Main). From the OH 18 cm absorption, observed with the Karl G. Jansky Very Large Array, we find that the line of sight magnetic field in this region is ∼0.13 mG. The same transitions in maser emission toward the neighbouring DR 21(OH) and W 75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use [C ii] 158 μm line and hydrogen radio recombination line data to constrain the physical conditions and the kinematics of the region. We find the OH column density to be ∼3.6 × 1016(Tex/25 K) cm−2, and that the 1665 and 1667 MHz absorption lines are originating from the gas where OH and C+ are co-existing in the PDR. Under reasonable assumptions, we find the measured magnetic field strength for the PDR to be lower than the value expected from the commonly discussed density–magnetic field relation while the field strength values estimated from the maser emission are roughly consistent with the same. Finally, we compare the magnetic field energy density with the overall energetics of DR 21’s PDR and find that, in its current evolutionary stage, the magnetic field is not dynamically important.

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

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.

scholarly journals The magnetic field of the Galaxy determined from the zeeman splitting of the 21-cm hydrogen line

1964 ◽  
Vol 20 ◽  
pp. 134-139
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Zeeman Effect ◽  
Mean Field ◽  
Neutral Hydrogen ◽  
Zeeman Splitting ◽  
Longitudinal Component ◽  
Frequency Separation ◽  
Intensity Difference ◽  
Interstellar Clouds ◽  
The Magnetic Field

The Zeeman effect can be used to measure directly the longitudinal component of the magnetic field in interstellar neutral hydrogen clouds. The frequency separation between the two circularly polarized components is 28 c/s for 10–5 G and can be inferred from measurements of the intensity difference between left- and right-hand circular polarization as a function of frequency. Earlier experiments at Jodrell Bank showed that the mean field in the interstellar medium was less than 10–5 G (Davies et al. 1960). Recent work using more sensitive techniques has provided a positive measurement of a weak general magnetic field and of fields of varying intensity in different interstellar clouds.

Quantum-Chemical calculations revealing the effects of magnetic fields on methanol masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 23-26
Author(s):  
Boy Lankhaar ◽  
Wouter Vlemmings ◽  
Gabriele Surcis ◽  
Huib Jan van Langevelde ◽  
Gerrit C. Groenenboom ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Circularly Polarized ◽  
Star Forming ◽  
Star Forming Regions ◽  
Polarized Emission ◽  
State Preference

AbstractMaser observations of both linearly and circularly polarized emission have provided unique information on the magnetic field in the densest parts of star forming regions, where non-maser magnetic field tracers are scarce. While linear polarization observations provide morphological constraints, magnetic field strengths are determined by measuring the Zeeman splitting in circularly polarized emission. Methanol is of special interest as it is one of the most abundant maser species and its different transitions probe unique areas around the protostar. However, its precise Zeeman-parameters are unknown. Experimental efforts to determine these Zeeman-parameters have failed. Here we present quantum-chemical calculations of the Zeeman-parameters of methanol, along with calculations of the hyperfine structure that are necessary to interpret the Zeeman effect in methanol. We use this model in re-analyzing methanol maser polarization observations. We discuss different mechanisms for hyperfine-state preference in the pumping of torsion-rotation transitions involved in the maser-action.

scholarly journals Maser polarization with ALMA

2012 ◽  
Vol 8 (S287) ◽  
pp. 64-68
Author(s):  
Andrés F. Pérez-Sánchez ◽  
Wouter Vlemmings
Keyword(s):  
Magnetic Field ◽  
Zeeman Splitting ◽  
Molecular State ◽  
Stimulated Emission ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Field Orientation ◽  
Maser Emission ◽  
Star Forming ◽  
The Magnetic Field

AbstractOnce ALMA full polarization capabilities are offered, (sub-)mm polarization studies will enter a new era. It will become possible to perform detailed studies of polarized maser emission towards for example massive star forming regions and late-type stars such as (post-) Asymptotic Giant Branch stars and young Planetary Nebulae. In these environments, SiO, H2O and HCN are molecules that can naturally generate polarized maser emission observable by ALMA. The maser polarization can then be used to derive the strength and morphology of the magnetic field in the masing regions. However, in order to derive, in particular, the magnetic field orientation from maser linear polarization, a number of conditions involving the rate of stimulated emission, molecular state decay and Zeeman splitting need to be satisfied. In this work, we discuss these conditions for the maser transitions in the ALMA frequency range and highlight the optimum transitions to further our understanding of star formation and evolved star magnetic fields.

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

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.

scholarly journals EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

2019 ◽  
Vol 623 ◽  
pp. A130 ◽  
Author(s):  
G. Surcis ◽  
W. H. T. Vlemmings ◽  
H. J. van Langevelde ◽  
B. Hutawarakorn Kramer ◽  
A. Bartkiewicz
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Limited Sample ◽  
Star Forming ◽  
Molecular Outflows ◽  
Star Forming Regions ◽  
The Magnetic Field

Context. Magnetohydrodynamical simulations show that the magnetic field can drive molecular outflows during the formation of massive protostars. The best probe to observationally measure both the morphology and the strength of this magnetic field at scales of 10–100 au is maser polarization. Aims. We measure the direction of magnetic fields at milliarcsecond resolution around a sample of massive star-forming regions to determine whether there is a relation between the orientation of the magnetic field and of the outflows. In addition, by estimating the magnetic field strength via the Zeeman splitting measurements, the role of magnetic field in the dynamics of the massive star-forming region is investigated. Methods. We selected a flux-limited sample of 31 massive star-forming regions to perform a statistical analysis of the magnetic field properties with respect to the molecular outflows characteristics. We report the linearly and circularly polarized emission of 6.7 GHz CH3OH masers towards seven massive star-forming regions of the total sample with the European VLBI Network. The sources are: G23.44−0.18, G25.83−0.18, G25.71−0.04, G28.31−0.39, G28.83−0.25, G29.96−0.02, and G43.80−0.13. Results. We identified a total of 219 CH3OH maser features, 47 and 2 of which showed linearly and circularly polarized emission, respectively. We measured well-ordered linear polarization vectors around all the massive young stellar objects and Zeeman splitting towards G25.71−0.04 and G28.83−0.25. Thanks to recent theoretical results, we were able to provide lower limits to the magnetic field strength from our Zeeman splitting measurements. Conclusions. We further confirm (based on ∼80% of the total flux-limited sample) that the magnetic field on scales of 10–100 au is preferentially oriented along the outflow axes. The estimated magnetic field strength of |B||| > 61 mG and >21 mG towards G25.71−0.04 and G28.83−0.25, respectively, indicates that it dominates the dynamics of the gas in both regions.

ZEEMAN SPLITTING OF DONOR STATES IN GERMANIUM

1958 ◽  
Vol 36 (9) ◽  
pp. 1161-1167 ◽  
Author(s):  
R. R. Haering
Keyword(s):  
Magnetic Field ◽  
Effective Mass ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Energy Difference ◽  
Band Energy ◽  
Mass Approximation ◽  
Donor States ◽  
Energy Surfaces ◽  
The Magnetic Field

The linear Zeeman effect of the 2p m = ± 1 donor states is calculated in the effective mass approximation. The resulting level splitting is independent of the longitudinal mass characterizing the ellipsoidal conduction band energy surfaces. This result is valid as long as the Zeeman splitting of the m = ±1 states is small compared to the energy difference between the 2p m = 0 and the 2p m = ± 1 states. The Zeeman pattern to be expected in germanium is plotted as a function of the angle between the magnetic field and the (100) direction.

scholarly journals Magnetic Field Structure of Star Forming Regions: VLBI Spectral Line Results

1984 ◽  
Vol 110 ◽  
pp. 333-334
Author(s):  
J.A. Garcia-Barreto ◽  
B. F. Burke ◽  
M. J. Reid ◽  
J. M. Moran ◽  
A. D. Haschick
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Aperture Synthesis ◽  
Stokes Parameters ◽  
Hii Region ◽  
Star Forming ◽  
Star Forming Regions ◽  
Vlbi Observations ◽  
The Magnetic Field ◽  
Synthesis Experiment

Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.

Sign in / Sign up

Export Citation Format

Share Document