▪ Abstract We discuss current observational and theoretical knowledge of magnetic fields, especially the large-scale structure in the disks and halos of spiral galaxies. Among other topics, we consider the enhancement of global magnetic fields in the interarm regions, magnetic spiral arms, and representations as superpositions of azimuthal modes, emphasizing a number of unresolved questions. It is argued that a turbulent hydromagnetic dynamo of some kind and an inverse cascade of magnetic energy gives the most plausible explanation for the regular galactic magnetic fields. Primordial theory is found to be unsatisfactory, and fields of cosmological origin may not even be able to provide a seed field for a dynamo. Although dynamo theory has its own problems, the general form of the dynamo equations appears quite robust. Finally, detailed models of magnetic field generation in galaxies, allowing for factors such as spiral structure, starbursts, galactic winds, and fountains, are discussed and confronted with...

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Galactic Magnetism: Recent developments and perspectives

We aim to summarize the current state of knowledge regarding Galactic Faraday rotation in an all-sky map of the Galactic Faraday depth. For this we have assembled the most extensive catalog of Faraday rotation data of compact extragalactic polarized radio sources to date. In the map-making procedure we used a recently developed algorithm that reconstructs the map and the power spectrum of a statistically isotropic and homogeneous field while taking into account uncertainties in the noise statistics. This procedure is able to identify some rotation angles that are offset by an integer multiple of π . The resulting map can be seen as an improved version of earlier such maps and is made publicly available, along with a map of its uncertainty. For the angular power spectrum we find a power law behavior C l  ∝ l -2.17 for a Faraday sky where an overall variance profile as a function of Galactic latitude has been removed, in agreement with earlier work. We show that this is in accordance with a 3D Fourier power spectrum P (k ) ∝ k -2.17 of the underlying field n e B r under simplifying geometrical and statistical assumptions.

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An improved map of the Galactic Faraday sky

The expected characteristics of the solar wind, extrapolated from the vicinity of the earth are described. Several models are examined for the interaction of the solar wind with the interstellar plasma and magnetic field. Various aspects of the penetration of neutral interstellar gas into the solar wind are considered. The dynamic effects of the neutral gas on the solar wind are described. Problems associated with the interaction of cosmic rays with the solar wind are discussed.

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The interaction of the solar wind with the interstellar medium

We have obtained 63 rotation measures (RMs) from polarization observations of southern pulsars, of which 54 are new measurements and three are varied from previous values. The new pulsar RM data at high Galactic latitudes are mostly consistent with the antisymmetric RM distribution found previously. For the Galactic disc, evidence for a field reversal near the Perseus arm, and possibly another beyond it, is presented. Inside the Solar Circle, in addition to the two known field reversals in or near the Carina–Sagittarius arm and the Crux–Scutum arm, a further reversal in the Norma arm is tentatively identified. These reversals, together with the pitch angle derived from pulsar RM and stellar polarization distributions, are consistent with bisymmetric spiral models for the large-scale magnetic field structure in the disc of our Galaxy. However, discrimination between models is complicated by the presence of smaller scale irregularities in the magnetic field, as well as uncertainties in the theoretical modelling.

Pulsar rotation measures and the magnetic structure of our Galaxy

The pulsation period of PSR 0833–45 is known to be gradually increasing, but between February 24 and March 3 the periodicity abruptly decreased by two parts per million.

Detection of a Change of State in the Pulsar PSR 0833-45

Measurements of the pulsar tentatively identified with the supernova remnant Vela X support the rotational model. This pulsar is remarkable for the very high degree of linear polarization in its signals.

Evidence in support of a rotational model for the pulsar PSR 0833-45

: The dependence on galactic latitude of the 11 and 20 cm polarization of 355 extragalactic sources reveals no definite evidence of depolarization within the Galaxy. The distribution of Faraday rotation can be explained in terms of a field along the local spiral arm, deformed by magnetic 'loops' in the solar neighbourhood. (Author)

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The Linear Polarization of Radio Sources Between 11 and 20 cm Wavelength. III. Influence of the Galaxy on Source Depolarization and Faraday Rotation

Observations are presented of the linear polarization of 366 sources observed with the Parkes 210 ft telescope at frequencies of 2650, 1660, and 1410 MHz. Parameters derived from the results, namely rotation measure, intrinsic polarization angle, and depolarization, are tabulated together with other pertinent physical properties. The source list includes 64 quasars, 119 radio or normal spiral galaxies, and 31 galactic objects; the remainder are unidentified objects or doubtful identifications.

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The Linear Polarization of Radio Sources Between 11 and 20 cm Wavelength. I. Observations

THE main features of the local magnetic field have been reasonably well established from determinations of the Faraday rotation of the polarized radiation from extra-galactic radio sources1–5. Previously, however, the projected density of observed sources on the sky has been too low to show fine structure in the field distribution. Between November 1963 and October 1966, with the Parkes 210-ft. telescope, determinations were made of the polarization of about 500 sources and we now have evidence for irregularities in the magnetic field in two directions of our Galaxy.

Evidence for an Association between Magnetic Field and Gas Outflow from a Spiral Arm

: Linear polarization measurements at 6 cm wavelength with the Parkes 210 ft telescope are given for 706 sources. Comparison of polarization parameters and flux densities with other published data is made. For the variable sources it is found that changes in polarized flux and position angle can accompany changes in intensity. (Author)

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D. Morris

Papers

Evidence in support of a rotational model for the pulsar PSR 0833-45

The Linear Polarization of Radio Sources Between 11 and 20 cm Wavelength. III. Influence of the Galaxy on Source Depolarization and Faraday Rotation

The Linear Polarization of Radio Sources Between 11 and 20 cm Wavelength. I. Observations

Evidence for an Association between Magnetic Field and Gas Outflow from a Spiral Arm

The Linear Polarization of Radio Sources at 6 cm Wavelength