scholarly journals Cosmic rays and magnetic fields in the core and halo of the starburst M82: implications for galactic wind physics

2020 ◽  
Vol 494 (2) ◽  
pp. 2679-2705 ◽  
Author(s):  
Benjamin J Buckman ◽  
Tim Linden ◽  
Todd A Thompson
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Large Scale ◽  
Gamma Ray ◽  
Minor Axis ◽  
Physical Parameters ◽  
Gas Density ◽  
Star Forming

ABSTRACT Cosmic rays (CRs) and magnetic fields may be dynamically important in driving large-scale galactic outflows from rapidly star-forming galaxies. We construct two-dimensional axisymmetric models of the local starburst and superwind galaxy M82 using the CR propagation code galprop. Using prescribed gas density and magnetic field distributions, wind profiles, CR injection rates, and stellar radiation fields, we simultaneously fit both the integrated gamma-ray emission and the spatially resolved multifrequency radio emission extended along M82’s minor axis. We explore the resulting constraints on the gas density, magnetic field strength, CR energy density, and the assumed CR advection profile. In accord with earlier one-zone studies, we generically find low central CR pressures, strong secondary electron/positron production, and an important role for relativistic bremsstrahlung losses in shaping the synchrotron spectrum. We find that the relatively low central CR density produces CR pressure gradients that are weak compared to gravity, strongly limiting the role of CRs in driving M82’s fast and mass-loaded galactic outflow. Our models require strong magnetic fields and advection speeds of the order of ∼1000 km s−1 on kpc scales along the minor axis in order to reproduce the extended radio emission. Degeneracies between the controlling physical parameters of the model and caveats to these findings are discussed.

scholarly journals The Formation of Discontinuities in Gas Flows in the ISM and its Relation to the Galactic Synchrotron Radio Emission

1990 ◽  
Vol 140 ◽  
pp. 159-162
Author(s):  
V.G. Berman ◽  
L.S. Marochnik ◽  
Yu.N. Mishurov ◽  
A.A. Suchkov
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Radio Emission ◽  
Large Scale ◽  
Field Energy ◽  
Gas Flows ◽  
Interstellar Gas ◽  
Gas Density ◽  
Magnetic Field Energy ◽  
Wide Range

We show that large–scale motions of the interstellar gas, such as those associated with galactic density waves, easily develop, over a wide range of scales, shocks and discontinuities which are expected to generate turbulence. The latter is supposed to evoke diffusion of magnetic fields and cosmic rays on scales down to a few parsecs. We suggest that these processes may be of major importance in discussions of interconnections between the observed radio emission of the disks of spiral galaxies and the gas density distribution within them. In particular, we predict that the density of cosmic rays and magnetic field energy must be much less contrasted (on scales of ~1 pc and up to the scales of galactic shocks) than the gas density, hence the synchrotron radio emission is not as contrasted as is predicted under the hypothesis of a fully frozen-in magnetic field.

Methanol masers and magnetic field in IRAS18089-1732

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.

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 Observational signatures of magnetic field structure in relativistic AGN jets

2019 ◽  
Vol 622 ◽  
pp. A122 ◽  
Author(s):  
Christopher Prior ◽  
Konstantinos N. Gourgouliatos
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Faraday Rotation ◽  
Large Scale ◽  
Field Structure ◽  
Synchrotron Emission ◽  
Supermassive Black Hole ◽  
Rotation Measure

Context. Active galactic nuclei (AGN) launch highly energetic jets sometimes outshining their host galaxy. These jets are collimated outflows that have been accelerated near a supermassive black hole located at the centre of the galaxy. Their, virtually indispensable, energy reservoir is either due to gravitational energy released from accretion or due to the extraction of kinetic energy from the rotating supermassive black hole itself. In order to channel part of this energy to the jet, though, the presence of magnetic fields is necessary. The extent to which these magnetic fields survive in the jet further from the launching region is under debate. Nevertheless, observations of polarised emission and Faraday rotation measure confirm the existence of large scale magnetic fields in jets. Aims. Various models describing the origin of the magnetic fields in AGN jets lead to different predictions about the large scale structure of the magnetic field. In this paper we study the observational signatures of different magnetic field configurations that may exist in AGN jets in order to asses what kind of information regarding the field structure can be obtained from radio emission, and what would be missed. Methods. We explore three families of magnetic field configurations. First, a force-free helical magnetic field corresponding to a dynamically relaxed field in the rest frame of the jet. Second, a magnetic field with a co-axial cable structure arising from the Biermann-battery effect at the accretion disk. Third, a braided magnetic field that could be generated by turbulent motion at the accretion disk. We evaluate the intensity of synchrotron emission, the intrinsic polarization profile and the Faraday rotation measure arising from these fields. We assume that the jet consists of a relativistic spine where the radiation originates from and a sheath containing thermalised electrons responsible for the Faraday screening. We evaluate these values for a range of viewing angles and Lorentz factors. We account for Gaussian beaming that smooths the observed profile. Results. Radio emission distributions from the jets with dominant large-scale helical fields show asymmetry across their width. The Faraday rotation asymmetry is the same for fields with opposing chirality (handedness). For jets which are tilted towards the observer the synchrotron emission and fractional polarization can distinguish the field’s chirality. When viewed either side-on or at a Blazar type angle only the fractional polarization can make this distinction. Further this distinction can only be made if the direction of the jet propagation velocity is known, along with the location of the jet’s origin. The complex structure of the braided field is found not to be observable due to a combination of line of sight integration and limited resolution of observation. This raises the possibility that, even if asymmetric radio emission signatures are present, the true structure of the field may still be obscure.

scholarly journals High-energy processes in starburst-driven winds

2020 ◽  
Vol 496 (2) ◽  
pp. 2474-2481 ◽  
Author(s):  
Ana L Müller ◽  
Gustavo E Romero ◽  
Markus Roth
Keyword(s):  
Cosmic Rays ◽  
Power Law ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
X Ray ◽  
Star Forming ◽  
Star Forming Regions ◽  
Energy Processes ◽  
Relativistic Particles

ABSTRACT Starburst galaxies generate large-scale winds powered by the activity in the star-forming regions located in the galactic discs. Fragmentation of the disc produced by the outbreak of the wind results in the formation of clouds. Bowshocks caused by the supersonic outflow appear around such clouds. In this paper, we discuss the acceleration of relativistic particles and the production of non-thermal radiation in such scenario. Cosmic rays accelerated at the bowshocks do not reach the highest energies, although the high-energy luminosity generated is significant. We show that up to ∼10 per cent of the gamma-ray emission in starbursts might come from these sources outside the galactic discs. Discrete X-ray sources with a power-law component are also expected.

scholarly journals CHANG-ES

2019 ◽  
Vol 623 ◽  
pp. A33 ◽  
Author(s):  
Y. Stein ◽  
R.-J. Dettmar ◽  
J. Irwin ◽  
R. Beck ◽  
M. Weżgowiec ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Cosmic Ray ◽  
Transport Processes ◽  
X Ray ◽  
Radio Data ◽  
The Magnetic Field

Context. The observation of total and linearly polarized synchrotron radiation of spiral galaxies in the radio continuum reveals the distribution and structure of their magnetic fields. By observing these, information about the proposed dynamo processes that preserve the large-scale magnetic fields in spiral galaxies can be gained. Additionally, by analyzing the synchrotron intensity, the transport processes of cosmic rays into the halo of edge-on spiral galaxies can be investigated. Aims. We analyze the magnetic field geometry and the transport processes of the cosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band). Supplementary X-ray data are used to investigate the hot gas in NGC 4666. Methods. We determine the radio scale heights of total power emission at both frequencies for this galaxy. We show the magnetic field orientations derived from the polarization data. Using rotation measure (RM) synthesis we further study the behavior of the RM values along the disk in C-band to investigate the large-scale magnetic-field pattern. We use the revised equipartition formula to calculate a map of the magnetic field strength. Furthermore, we model the processes of cosmic-ray transport into the halo with the 1D SPINNAKER model. Results. The extended radio halo of NGC 4666 is box-shaped and is probably produced by the previously observed supernova-driven superwind. This is supported by our finding of an advective cosmic-ray transport such as that expected for a galactic wind. The scale-height analysis revealed an asymmetric halo above and below the disk as well as between the two sides of the major axis. A central point source as well as a bubble structure is seen in the radio data for the first time. Our X-ray data show a box-shaped hot halo around NGC 4666 and furthermore confirm the AGN nature of the central source. NGC 4666 has a large-scale X-shaped magnetic field in the halo, as has been observed in other edge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666 shows hints of field reversals along its radius, which is the first detection of this phenomenon in an external galaxy.

scholarly journals Constraints on the Magnetic Fields in Galaxies Implied by the Infrared-to-Radio Correlation

1990 ◽  
Vol 140 ◽  
pp. 239-240 ◽  
Author(s):  
George Helou ◽  
M. D. Bicay
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Physical Model ◽  
Magnetic Field Strength ◽  
Far Infrared ◽  
Universal Relation ◽  
Gas Density ◽  
Star Forming ◽  
Tight Correlation

We propose a physical model for understanding the tight correlation between far-infrared and non-thermal radio luminosities in star-forming galaxies. This approach suggests that the only constraint implied by the correlation is a universal relation whereby magnetic field strength scales with gas density to a power 1/3≤β≤<2/3.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

scholarly journals The measurement of the energy of cosmic rays - II—The curvature measurements and the energy spectrum

1936 ◽  
Vol 154 (883) ◽  
pp. 573-587 ◽  
Keyword(s):  
Magnetic Field ◽  
Energy Spectrum ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Strong Magnetic Fields ◽  
The Earth ◽  
Primary Particles ◽  
Curvature Measurements

Both the penetrating power of the cosmic rays through material ab­sorbers and their ability to reach the earth in spite of its magnetic field, make it certain that the energy of many of the primary particles must reach at least 10 11 e-volts. However, the energy measurements by Kunze, and by Anderson, using cloud chambers in strong magnetic fields, have extended only to about 5 x 10 9 e-volts. Particles of greater energy were reported, but the curvature of their tracks was too small to be measured with certainty. We have extended these energy measurements to somewhat higher energies, using a large electro-magnet specially built for the purpose and described in Part I. As used in these experiments, the magnet allowed the photography of tracks 17 cm long in a field of about 14,000 gauss. The magnet weighed about 11,000 kilos and used a power of 25 kilowatts.

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

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