Velocity field in the galactic plane

In this paper we present a study of the velocity components of the local centroids in the galactic plane for a point-axial stellar system model in a non-stationary state and with an equatorial plane of symmetry. The main results obtained are:(1) A displacement and attenuation of the maximum of the velocity-distance curve for different values of the direction. (2) The existence of expansion and contraction zones in the galactic plane.It must be pointed out that, in general, these velocity-distance curves require corrections due to the inclination of the galaxy. In the same way, it would be necessary to integrate the light along the line of vision. In the cylindrical case this latter factor has been studied by Catala (1975). However, these corrections do not greatly affect the structural form of the rotation curve as far as the aspects dealt with in this paper are concerned.     

On the structure of the magnetic field near a black hole in active galactic nuclei

Using the Grad-Shafranov equation, we consider a new analytical model of the black hole magnetosphere based on the assumption that the magnetic field is radial near the horizon and uniform (cylindrical) in the jet region. Within this model, we have managed to show that the angular velocity of particles Ω_F near the rotation axis of the black hole can be smaller than Ω_H/2. This result is consistent with the latest numerical simulations.     

Unusual enhancement of galactic cosmic-ray intensity near an interplanetary magnetic field annihilation region

The ground level cosmic-ray intensity enhancement on September 18, 1979 is analysed by combining neutron monitor data with simultaneous in situ interplanetary measurements. An explanation of the increase with respect to local acceleration process, alternate to that suggested by Agrawal and Venkatesan (1982), is given in connection with the effect of a magnetic field annihilation region.     

The distribution of interstellar dust in nine regions near the galactic plane

In dem vorliegenden Artikel werden die interstellare Extinktion und die Verteilung des interstellaren Staubes bis zu einer Entfernung von 8–10 kpc untersucht. Die Messungen erfolgten in der galaktischen Länge von 7° bis 222° in Richtung der offenen Sternhaufen NGC 6531, NGC 6866, Tr 35, NGC 7062, NGC 7654, IC 1805, NGC 1664, NGC 2251 und NGC 2323.     

Extragalactic cosmic rays and the galactic magnetic field

The origin and behavior of cosmic rays in the Galaxy depends crucially upon whether the galactic magnetic field has a closed topology, as does the field of Earth, or whether a major fraction of the lines of force connect into extragalactic space. If the latter, then cosmic rays could be of extragalactic origin, or they could be of galactic origin, detained in the Galaxy by the scattering offered by hydromagnetic waves, etc. If, on the other hand, the field is largely closed, then cosmic rays cannot be of extragalactic origin (at least below 10¹⁶ eV). They must be of galactic origin and escape because their collective pressure inflates the galactic field and they push their way out.This paper examines the structure of a galactic field that opens initially into intergalactic space and, with the inclusion of turbulent diffusion, finds no possibility for maintaining a significant magnetic connection with an extragalactic field. Unless some mechanism can be found, we are forced to the conclusion that the field is closed, that cosmic rays are of galactic origin, and that cosmic rays escape from the Galaxy only by pushing their way out.     

The origin of our galactic magnetic field

A serious difficulty with the standard alpha‐omega theory of the origin of galactic magnetic fields involves the question of flux expulsion. This is intimately related to flux freezing. The alpha‐omega theory is shown in the context of the giant superbubble explosions that have a large impact on the physics of the interstellar medium. It is shown that superbubbles alone can duplicate the processes of the alpha‐omega dynamo and produce exponential growth of the galactic magnetic field. The possibility of the blow‐out of pieces of the magnetic field is discussed and it is shown that they have the potential to solve the flux‐expulsion problem. However, such an explanation must lead to apparent ‘gaps’ in the field in the galactic disc. These gaps are probably unavoidable in any dynamo theory and should have important observable consequences, one of which is an explanation for the escape of cosmic rays from the disc (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interpretation of faraday rotation in the galactic magnetic field

The autocorrelation function of Faraday rotation measures is discussed in terms of different types of galactic field configurations. The autocorrelation function evaluated from published data of 139 radio galaxies and quasars is found to resemble a form typical for a quasi-longitudinal field, whereas the autocorrelation function of 38 pulsars turns out to be of the form expected for a longitudinal field. These observations are interpreted with respect to the position of the solar system relative to the neutral sheet in a quasi-longitudinal field configuration.Rotation measures calculated theoretically using a mathematical formulation of the quasi-longitudinal field model are adapted to experimental data. The resulting polarity of the global field structure is discussed in connection with the original dipole-like configuration the magnetic momentum vector of which is found to have been antiparallel to the angular momentum vector of the Galaxy. The relation between the field strength and the density of electrons is found to be consistent with earlier results.     

WSRT observations of radio sources in the galactic plane near l =54°

A radio continuum map of a 1°5 X 1°5 region in the galactic plane nearl = 54° is presented at 49 cm with a resolution of 100 arcsec X 200 arcsec. The shell source G 54.4 - 0.3 has the characteristics of a supernova remnant while the second large ring structure G 53.9 + 0.3 is a Hn ring consisting of W 52 and several small-diameter thermal sources. One of the twelve small-diameter sources (G 54.73 + 0.61) has a spectral index⇏ -1.6.     

Hierarchial galactic dynamo and seed magnetic field problem

A new approach to the galactic seed magnetic field problem is briefly discussed. It is shown that, in early stages of galactic evolution, the hierarchial agglomeration and fragmentation processes can account for the generation of a dynamically important magnetic field. The amplification of this field follows an inverse cascade since a non-zero average value of the field amplified on a smaller scale serves as a seed field on the next (earlier) hierarchial scale. In such a scenario, a problem of how to get things started never occurs as any infinitesimally small battery generated seed field (Lazarian 1992a) can be efficiently amplified passing by through a sufficient number of amplification cascades.     

Maintenance of spiral arms and galactic magnetic field configurations

Of the various proposed mechanisms to maintain spiral arms in spiral galaxies, three have been supported by observations, statistics, or theories (bar, companion, extended solid-body rotation curve). It is shown here that in the presence of a central bar or oval distirtion to maintain spiral arms, the global magnetic field lines also follow the spiral shape of the arms. Excluding then barred galaxies, it is confirmed that in the presence of a companion galaxy to maintain spiral arms, the global magnetic lines in a spiral galaxy will either follow thespiral shape of the arms (when tides are larger), or else will follow thering shape of the orbit of matter crossing spiral arms (when tides are small). In the presence of an extended solid-body rotation curve to maintain spiral arms within the solid-body rotation region, the global magnetic field lines also follow the spiral shape of the arms.The results above do not favour the hypothesis that a weak intergalactic magnetic field could have been amplified enough by gravitational contraction of a protogalaxy to give rise to the observed strength of galactic magnetic fields. On the contrary, leakage of galactic magnetic fields into intergalactic/cosmological space is expected.     

Inverse problem for determining the potential and velocity field in the galactic plane

Leningrad State University. Translated from Astrofizika, Vol. 30, No. 3, pp. 643–653, May–June, 1989.     

Orientation of the galactic magnetic field in the vicinity of the solar system

It is found from analysis of the position angles of the plane of polarization of about 3000 stars (¦b¦ 5° andP 0.5%) that the angle between the magnetic field and the equatorial plane of the galaxy is approximately 0–5°. The distance within which the local magnetic fields of the galaxy have a greater effect on the position angles of the plane of polarization than the galactic magnetic field is estimated to be about 500 pc. The effect of the galactic magnetic field becomes dominant for distancesr 1000 pc.Translated fromAstrofizika, Vol. 39, No. 4, pp. 553–559, November, 1996.     

The interstellar magnetic field near the Galactic center

We review the current observational knowledge of the interstellar magnetic field within ∼150 pc ofthe Galactic center. We also discuss the various theoretical scenarios that have been put forward to explain the existing observations. Our critical overview leads to two important conclusions: (1) The interstellar magnetic field near the GC is approximately poloidal on average in the diffuse intercloud medium and approximately horizontal in dense interstellar clouds. (2) In the general intercloud medium, the field is relatively weak and probably close to equipartition with cosmic rays (B ∼ (6–20) μ G), but there exist a number of localized filaments where the field is much stronger (some filaments could possibly have B ≳ 1 mG). In dense interstellar clouds, the field is probably rather strong, with typical values ranging between a few 0.1 mG and a few mG (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An UV survey of the galactic plane

The present paper is the introduction to a systematic analysis of 123 6-degree fields near the galactic plane, recorded in the medium ultraviolet (2000 Å) by the ballon-borne experiment SCAP 2000 of the Laboratoire d'Astronomie Spatiale, Marseille, and Geneva Observatory. The available data are presented and the general properties of the images are briefly discussed.It is shown that the high selectivity of the UV passband regarding spectral type, together with the strong interstellar extinction at that wavelength, provide the necessary conditions for an efficient application of Wolf's method to study the distribution of interstellar matter in the solar neighbourhood. The results of a fast analysis of the available data are presented here.     

The near earth magnetic field of the magnetotail current

In the forward part of the magnetosphere the distant tail current system approximates a magnetic quadrupole composed of two distorted adjacent solenoids. The current in the neutral sheet at this distance is accurately approximated as an infinitesimally thin current sheet. We have calculated the magnetic field near the Earth by integrating over the entire tail current system assuming the magnetotail is a cylinder of constant radius and that the tail current decreases with distance into the tail as $\text{|x|}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}$. The field is then represented by a scalar potential expanded into spherical harmonics which may be conveniently added to the spherical harmonic expansion of the scalar potential representing the magnetopause current system.