Structural details of the Sagittarius A complex - Evidence for a large-scale poloidal magnetic field in the Galactic center region

Context. Cosmic-ray propagation is strongly dependent on the large-scale configuration of the Galactic magnetic field. In particular, the Galactic center region provides highly interesting cosmic-ray data from gamma-ray maps and it is clear that a large fraction of the cosmic rays detected at Earth originate in this region of the Galaxy. Yet because of confusion from line-of-sight integration, the magnetic field structure in the Galactic center is not well known and no large-scale magnetic field model exists at present. Aims. In this paper, we develop a magnetic field model, derived from observational data on the diffuse gas, nonthermal radio filaments, and molecular clouds. Methods. We derive an analytical description of the magnetic field structure in the central molecular zone by combining observational data with the theoretical modeling of the basic properties of magnetic fields. Results. We provide a first description of the large-scale magnetic field in the Galactic center region. We present first test simulations of cosmic-ray propagation and the impact of the magnetic field structure on the cosmic-ray distribution in the three dimensions. Conclusions. Our magnetic field model is able to describe the main features of polarization maps; it is particularly important to note that they are significantly better than standard global Galactic magnetic field models. It can also be used to model cosmic-ray propagation in the Galactic center region more accurately.

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Cloud–cloud collision in the Galactic Center Arc

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa095 ◽

2020 ◽

Author(s):

Masato Tsuboi ◽

Yoshimi Kitamura ◽

Kenta Uehara ◽

Ryosuke Miyawaki ◽

Takahiro Tsutsumi ◽

...

Keyword(s):

Magnetic Field ◽

Emission Line ◽

Molecular Cloud ◽

Galactic Center ◽

Compact Objects ◽

Emission Lines ◽

Common Mechanism ◽

Poloidal Magnetic Field ◽

Sagittarius A ◽

Vertical Part

Abstract We performed a search of cloud–cloud collision (CCC) sites in the Sagittarius A molecular cloud (SgrAMC) based on the survey observations using the Nobeyama 45 m telescope in the C32S J = 1–0 and SiO v = 0 J = 2–1 emission lines. We found candidates abundant in shocked molecular gas in the Galactic Center Arc (GCA). One of them, M0.014−0.054, is located in the mapping area of our previous ALMA mosaic observation. We explored the structure and kinematics of M0.014−0.054 in the C32S J = 2–1, C34S J = 2–1, SiO v = 0 J = 2–1, H13CO+J = 1–0, and SO N, J = 2, 2–1, 1 emission lines and fainter emission lines. M0.014−0.054 is likely formed by the CCC between the vertical molecular filaments (the “vertical part,” or VP) of the GCA, and other molecular filaments along Galactic longitude. The bridging features between these colliding filaments on the PV diagram are found, which are the characteristics expected in CCC sites. We also found continuum compact objects in M0.014−0.054, which have no counterpart in the H42α recombination line. They are detected in the SO emission line, and would be “hot molecular cores” (HMCs). Because the local thermodynamic equilibrium mass of one HMC is larger than the virial mass, it is bound gravitationally. This is also detected in the CCS emission line. The embedded star would be too young to ionize the surrounding molecular cloud. The VP is traced by a poloidal magnetic field. Because the strength of the magnetic field is estimated to be ∼mgauss using the Chandrasekhar–Fermi method, the VP is supported against fragmentation. The star formation in the HMC of M0.014−0.054 is likely induced by the CCC between the stable filaments, which may be a common mechanism in the SgrAMC.

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On the dynamical interaction between overshooting convection and an underlying dipole magnetic field – I. The non-dynamo regime

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab477 ◽

2021 ◽

Vol 503 (1) ◽

pp. 362-375

Author(s):

L Korre ◽

NH Brummell ◽

P Garaud ◽

C Guervilly

Keyword(s):

Magnetic Field ◽

Turbulent Diffusion ◽

Large Scale ◽

Molecular Diffusion ◽

Mean Field ◽

Stable Region ◽

Turbulent Regime ◽

Poloidal Magnetic Field ◽

Dynamical Interaction ◽

Large Scale Field

ABSTRACT Motivated by the dynamics in the deep interiors of many stars, we study the interaction between overshooting convection and the large-scale poloidal fields residing in radiative zones. We have run a suite of 3D Boussinesq numerical calculations in a spherical shell that consists of a convection zone with an underlying stable region that initially compactly contains a dipole field. By varying the strength of the convective driving, we find that, in the less turbulent regime, convection acts as turbulent diffusion that removes the field faster than solely molecular diffusion would do. However, in the more turbulent regime, turbulent pumping becomes more efficient and partially counteracts turbulent diffusion, leading to a local accumulation of the field below the overshoot region. These simulations suggest that dipole fields might be confined in underlying stable regions by highly turbulent convective motions at stellar parameters. The confinement is of large-scale field in an average sense and we show that it is reasonably modelled by mean-field ideas. Our findings are particularly interesting for certain models of the Sun, which require a large-scale, poloidal magnetic field to be confined in the solar radiative zone in order to explain simultaneously the uniform rotation of the latter and the thinness of the solar tachocline.

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Near-infrared Polarimetry and Interstellar Magnetic Fields in the Galactic Center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314011569 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 387-387

Author(s):

S. Nishiyama ◽

H. Hatano ◽

T. Nagata ◽

M. Tamura

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Near Infrared ◽

Galactic Center ◽

Smooth Transition ◽

The Magnetic Field

AbstractWe present a large-scale view of the magnetic field (MF) in the central 3° × 2° region of our Galaxy. There is a smooth transition of the large-scale MF configuration in this region.

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Characterizing the dynamo in a radiatively inefficient accretion flow

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa996 ◽

2020 ◽

Vol 494 (4) ◽

pp. 4854-4866 ◽

Cited By ~ 1

Author(s):

Prasun Dhang ◽

Abhijit Bendre ◽

Prateek Sharma ◽

Kandaswamy Subramanian

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Mean Field ◽

Compact Object ◽

Rotational Instability ◽

Test Field ◽

Poloidal Magnetic Field ◽

Accretion Flow ◽

The Mean ◽

Value Decomposition

ABSTRACT We explore the magneto-rotational instability (MRI)-driven dynamo in a radiatively inefficient accretion flow (RIAF) using the mean field dynamo paradigm. Using singular value decomposition (SVD) we obtain the least-squares fitting dynamo coefficients α and γ by comparing the time series of the turbulent electromotive force and the mean magnetic field. Our study is the first one to show the poloidal distribution of these dynamo coefficients in global accretion flow simulations. Surprisingly, we obtain a high value of the turbulent pumping coefficient γ, which transports the mean magnetic flux radially outwards. This would have implications for the launching of magnetized jets that are produced efficiently in presence a large-scale poloidal magnetic field close to the compact object. We present a scenario of a truncated disc beyond the RIAF where a large-scale dynamo-generated poloidal magnetic field can aid jet launching close to the black hole. Magnitude of all the calculated coefficients decreases with radius. Meridional variations of αϕϕ, responsible for toroidal to poloidal field conversion, is very similar to that found in shearing box simulations using the ‘test field’ (TF) method. By estimating the relative importance of α-effect and shear, we conclude that the MRI-driven large-scale dynamo, which operates at high latitudes beyond a disc scale height, is essentially of the α − Ω type.

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The geometry of the magnetic field in the central molecular zone measured by PILOT

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935072 ◽

2019 ◽

Vol 630 ◽

pp. A74 ◽

Cited By ~ 7

Author(s):

A. Mangilli ◽

J. Aumont ◽

J.-Ph. Bernard ◽

A. Buzzelli ◽

G. de Gasperis ◽

...

Keyword(s):

Magnetic Field ◽

Molecular Clouds ◽

Angular Resolution ◽

Galactic Center ◽

Galactic Plane ◽

Mean Field ◽

Field Orientation ◽

Center Region ◽

The Mean ◽

The Magnetic Field

We present the first far infrared (FIR) dust emission polarization map covering the full extent of Milky Way’s central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic center region − 2° < ℓ < 2°, − 4° < b < 3° at a wavelength of 240 μm and an angular resolution of 2.2′. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky (POS) that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of ≃22° clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonally to the field traced by GHz radio synchrotron emission in the Galactic center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 and 50 km s−1 molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. The low polarization fraction in the Galactic center region measured with Planck at 353 GHz combined with a highly ordered projected field orientation is unusual. This feature actually extends to the whole inner Galactic plane. We propose that it could be caused by the increased number of turbulent cells for the long lines of sight towards the inner Galactic plane or to dust properties specific to the inner regions of the Galaxy. Assuming equipartition between magnetic pressure and ram pressure, we obtain magnetic field strength estimates of the order of 1 mG for several CMZ molecular clouds.

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The Toroidal Magnetic Field inside the Sun

International Astronomical Union Colloquium ◽

10.1017/s0252921100079616 ◽

1991 ◽

Vol 130 ◽

pp. 187-189

Author(s):

V.N. Krivodubskij ◽

A.E. Dudorov ◽

A.A. Ruzmaikin ◽

T.V. Ruzmaikina

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Convection Zone ◽

The Sun ◽

Poloidal Magnetic Field ◽

Radial Gradient ◽

The Core ◽

Large Scale Magnetic Field ◽

Magnetic Buoyancy ◽

The Magnetic Field

Analysis of the fine structure of the solar oscillations has enabled us to determine the internal rotation of the Sun and to estimate the magnitude of the large-scale magnetic field inside the Sun. According to the data of Duvall et al. (1984), the core of the Sun rotates about twice as fast as the solar surface. Recently Dziembowski et al. (1989) have showed that there is a sharp radial gradient in the Sun’s rotation at the base of the convection zone, near the boundary with the radiative interior. It seems to us that the sharp radial gradients of the angular velocity near the core of the Sun and at the base of the convection zone, acting on the relict poloidal magnetic field Br, must excite an intense toroidal field Bф, that can compensate for the loss of the magnetic field due to magnetic buoyancy.

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Large-Scale Internal Magnetic Field of the Sun

Symposium - International Astronomical Union ◽

10.1017/s0074180900044399 ◽

1990 ◽

Vol 138 ◽

pp. 391-394

Author(s):

A.E. Dudorov ◽

V.N. Krivodubskij ◽

A.A. Ruzmaikin ◽

T.V. Ruzmaikina

Keyword(s):

Magnetic Field ◽

Differential Rotation ◽

Large Scale ◽

The Sun ◽

Poloidal Magnetic Field ◽

The Core ◽

Torsional Waves ◽

Formation And Evolution ◽

Field Lines ◽

The Magnetic Field

The behaviour of the magnetic field during the formation and evolution of the Sun is investigated. It is shown that an internal poloidal magnetic field of the order of 104 − 105 G near the core of the Sun may be compatible with differential rotation and with torsional waves, travelling along the magnetic field lines (Dudorov et al., 1989).

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A large scale CO survey of the Galactic center region

Astronomy and Astrophysics Supplement Series ◽

10.1051/aas:1997214 ◽

1997 ◽

Vol 125 (1) ◽

pp. 99-138 ◽

Cited By ~ 60

Author(s):

M. Bitran ◽

H. Alvarez ◽

L. Bronfman ◽

J. May ◽

P. Thaddeus

Keyword(s):

Large Scale ◽

Galactic Center ◽

Center Region

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Interplay between magnetic fields and differential rotation in a stably stratified stellar radiative zone

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037828 ◽

2020 ◽

Vol 641 ◽

pp. A13 ◽

Cited By ~ 1

Author(s):

L. Jouve ◽

F. Lignières ◽

M. Gaurat

Keyword(s):

Magnetic Field ◽

Differential Rotation ◽

Large Scale ◽

Stable Stratification ◽

Rotational Instability ◽

Intermediate Mass ◽

Poloidal Magnetic Field ◽

Giant Stars ◽

Radiative Zone ◽

Red Giant

Context. The interactions between magnetic fields and differential rotation in stellar radiative interiors could play a major role in achieving an understanding of the magnetism of intermediate-mass and massive stars and of the differential rotation profile observed in red-giant stars. Aims. The present study is aimed at studying the flow and field produced by a stellar radiative zone which is initially made to rotate differentially in the presence of a large-scale poloidal magnetic field threading the whole domain. We focus both on the axisymmetric configurations produced by the initial winding-up of the magnetic field lines and on the possible instabilities of those configurations. We investigate in detail the effects of the stable stratification and thermal diffusion and we aim, in particular, to assess the role of the stratification at stabilising the system. Methods. We performed 2D and 3D global Boussinesq numerical simulations started from an initial radial or cylindrical differential rotation and a large-scale poloidal magnetic field. Under the conditions of a large rotation frequency compared to the Alfvén frequency, we built a magnetic configuration strongly dominated by its toroidal component. We then perturbed this configuration to observe the development of non-axisymmetric instabilities. Results. The parameters of the simulations were chosen to respect the ordering of time scales of a typical stellar radiative zone. In this framework, the axisymmetric evolution is studied by varying the relative effects of the thermal diffusion, the Brunt-Väisälä frequency, the rotation, and the initial poloidal field strength. After a transient time and using a suitable adimensionalisation, we find that the axisymmetric state only depends on tes/tAp the ratio between the Eddington–Sweet circulation time scale and the Alfvén time scale. A scale analysis of the Boussinesq magnetohydrodynamical equations allows us to recover this result. In the cylindrical case, a magneto-rotational instability develops when the thermal diffusivity is sufficiently high to enable the favored wavenumbers to be insensitive to the effects of the stable stratification. In the radial case, the magneto-rotational instability is driven by the latitudinal shear created by the back-reaction of the Lorentz force on the flow. Increasing the level of stratification then leaves the growth rate of the instability mainly unaffected while its horizontal length scale grows. Conclusions. Non-axisymmetric instabilities are likely to exist in stellar radiative zones despite the stable stratification. They could be at the origin of the magnetic dichotomy observed in intermediate-mass and massive stars. They are also unavoidable candidates for the transport of angular momentum in red giant stars.

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