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Magnetic fields are found everywhere in the cosmic Universe. They have been known to exist on the Earth for centuries. They were detected in the Sun, measured in situ in the planets, observed in stars, galaxies and clusters of galaxies. Magnetic fields are responsible for many observed effects like radio continuum emission, jets, beamed emission in pulsars, star formation, etc. Possibly the whole universe is intimately governed by the presence of magnetic fields. This review will summarize the observational results and discuss the present interpretation for the origin of the magnetic fields.

I present a unique data set for the study of molecular gas in galaxies: a complete, high-resolution survey of the CO in M 31 and additional local studies. The fully sampled survey has an angular resolution of 23 FWHM and the interferometric data attain the pc-scale with sub-arcsecond resolution. For the first time it is now possible to study large and small scales in conjunction. Thus we are able to derive the global structure and study the links down to the individual cloud complexes and star formation regions.

Continuum observations of the edge-on spiral galaxy NGC 4945 with the Australia Telescope National Facility's Compact Array (ATCA) and the Parkes 64-m radio telescope are presented. The ATCA maps are currently the highest resolution wide-band radio continuum maps of this galaxy. A compact, non-thermal core of less than 60 pc diameter has been detected. The luminosity of the central 90 pc is 2 × 10 erg s, equivalent to almost half the total value of the galaxy. 90 per cent of the galaxy's λ = 3 cm radio emission originates from the nuclear bulge (central 4 kpc), the radio disc measuring 23 ± 2 kpc in diameter. The nuclear bulge of the galaxy has a spectral index of a = - 0.57 ± 0.04 (S ∝ v), similar to the core value. The disc emission of the galaxy has a much steeper spectral index of α= -1.1 ± 0.1, indicative of either a high-energy cut-off to the disc population of cosmic rays or differing source energetics in the disc. The large-scale radio morphology resembles that of the majority of edge-on spirals in that no radio halo has been detected. The average total equipartition magnetic field strength of the disc is 13 μG, whilst our polarization results indicate that the regular component of the magnetic field is about 3 μG. We conclude that NGC 4945 is one of a number of edge-on spiral galaxies with a magnetic field (and hence cosmic rays) confined to the disc.

The Sino-German 6cm polarization survey has mapped in total intensity and polarization intensity over an area of approximately 2200 square degrees in the Galactic disk. This survey provides an opportunity to search for Galactic supernova remnants (SNRs) that were previously unknown. We discovered the new SNRs G178.2-4.2 and G25.1-2.3 which have non-thermal spectra, using the 6cm data together with the observations with the Effelsberg telescope at 11 cm and 21 cm. Both G178.2-4.2 and G25.1-2.3 are faint and have an apparent diameter greater than 1deg. G178.2-4.2 shows a polarized shell. HI data suggest that G25.1-2.3 might have a distance of about 3 kpc. The 6cm survey data were also very important to identify two other new SNRs, G152.4-2.1 and G190.9-2.2., Comment: 4 pages, 3 figures, contributed talk at the IAU Symp. 296: Supernova Environmental Impacts

Magnetic fields are present in every corner of the Universe. The Earth, the Sun and most of the planets are known to possess dipolar magnetic fields. In the Galaxy many individual objects like stars, pulsars, bipolar nebulae and supernova remnants are found to have associated magnetic fields. It seems that the rotation plays a significant role in the ability of a cosmic object to develop a magnetic field. The magnetic field of the Galaxy is observed to be oriented along the galactic plane as evidenced by both optical and radio polarization observations. Radio maps of the Galactic centre reveal poloidal magnetic fields as ‘wisps’ or ‘strings’ around Sagittarius A. Observations of nearby galaxies give us remarkable information about the large-scale magnetic fields in these building blocks of the Universe. Magnetic fields play an important role in the formation of jets of radio galaxies. Further out, in clusters of galaxies, definitive evidence has been given for the existence of intergalactic magnetic fields.

Un modele simple est developpe pour l'origine des anneaux de gaz moleculaire des regions centrales de galaxies. Les galaxies sont considerees comme constituees d'une region centrale avec une rotation de corps solide et d'un disque en rotation differentielle. Le transport du moment cinetique visqueux dans le disque est analyse

We present high quality polarimetric observations with the Effelsberg radio telescope of the Crab pulsar at 8.35 GHz using a new sensitive receiver with a very large bandwidth. We present our observations and discuss them in the context of the conclusions reached by Moffett & Hankins (1999) about the geometry and the origin of the various pulse components.

We have observed the continuum emission of the interacting galaxy NGC4631 at 0.87 and 1.23mm using the Heinrich-Hertz-Telescope on Mt. Graham and the IRAM 30-m telescope on Pico Veleta. We have obtained fully sampled maps which cover the optical emission out to a radius of about 7' at both wavelengths. For a detailed analysis, we carefully subtracted the line contributions and synchrotron and free-free emission from the data, which added up to 6% at 1.23mm and 10% at 0.87mm. We combined the flux densities with FIR data to obtain dust spectra and calculate dust temperatures, absorption cross sections, and masses. Assuming a ``standard'' dust model, which consists of two populations of big grains at moderate and warm temperatures, we obtained temperatures of 18K and 50K for the both components. However, such a model suffers from an excess of the radiation at 1.23mm, and the dust absorption cross section seems to be enhanced by a factor 3 compared to previous results and theoretical expectations. At large galactocentric radii, where the galaxy shows disturbances as a result of gravitational interaction, this effect seems to be even stronger. Some possibilities to resolve these problems are discussed. The data could be explained by a very cold dust component at a temperature of 4-6K, an increased abundance of very small grains, or a component of grains with unusual optical properties. We favour the latter possibility, since the first two lead to inconsistencies., 12 pages, 6 figures, accepted for publication in Astronomy & Astrophysics. Updated version with minor errors corrected (typos, LaTeX formatting, missing citation)

The late-type edge-on spiral galaxy NGC 4631 is known for its high star formation rate and extended radio halo with a uniform magnetic field component ordered predominantly perpendicular to the plane of the galaxy in the inner 6 kpc (assuming a distance of 7.5 Mpc, 1′ = 2.2 kpc) (Hummel et al. 1988; Golla, Ph.D., in preparation). The strongest radio continuum source of NGC 4631 is located at the eastern edge of the central region near a giant HII region complex CM67 (Crillon and Monnet 1969). The magnetic field orientation going out from the central region and especially from the region CM67 as well as the prominent north eastern low frequency radio spur (cf. Hummel et al. 1991) indicate a close connection between the synchrotron emission of the radio halo of NGC 4631 and star forming regions/CM67 in the disk (Golla and Hummel, in preparation). Probably cosmic rays from star forming regions in the disk propagate along the magnetic field Unes into the halo.

Cosmic magnetic fields have now been studied for over 100 years. Although the initial detection was done at optical wavelengths, it was radio astronomy that gave us the bulk of information on cosmic magnetic fields in the recent years. In this review the observational results obtained by radio astronomy methods will be discussed. In particular maps of Galactic magnetic fields as well as magnetic fields in nearby galaxies will be presented. A discussion of possible developments in the near future will conclude this review.

To measure radio polarization one needs to analyze the incoming wave by means of a polarimeter. This is the crucial device that allows to determine the Stokes parameters after abstraction of the incoming wave in two orthogonal planes. The development of polarimeters in Effelsberg over the past 30 years is described in the present paper.

The structure of the Large Magellanic Cloud (LMC) has posed many questions and has led to many controversial discussions. Although classified as an 'irregular', repeated claims have been made suggesting that the LMC has spiral structure. Furthermore, this 'spiral' structure seems to originate in the 30-Doradus nebula which, as a result, was sometimes referred to as the 'nucleus' of the LMC. We summarize the recent data on the LMC and re-examine the HI data to point out that possibly different rotation centres exist for different components.

I present the results of recent 9 mm observations of the starburst galaxy M 82 with the Effelsberg 100-m radio telescope. The magnetic fields deduced from these observations are in good agreement with previous multifrequency VLA observations. The general pattern of azimuthal magnetic fields along the disc of the galaxy and vertical fields in the central region, as seen in most nearby galaxies, is confirmed to exist also in M 82. Since the starburst galaxy M 82 is a very powerful radio source similar objects should be visible at large distances. Possibly the distant magnetic Universe could be probed by observing sources similar to M 82 with the new generation of radio telescopes. Here the ALMA telescope holds great promise for the near future. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In the framework of our multi-frequency study of Virgo A we have performed observations of Vir A at 10.55 GHz with the Effelsberg 100-m telescope. Using our improved CLEAN procedure for single dish data we have increased the dynamic range to some 40 dB.

The Revised Shapley-Ames Catalog (Sandage & Tamman, 1981) contains 335 spiral galaxies brighter than BT = 12. A subsample of these galaxies with δ ≥ -25° and total flux densities at 1.49 GHz (Condon, 1987) above 10 mJy were observed at λ2.8 cm using the 100-m radio telescope of the MPIfR Bonn. Depending on the expected flux density and extent of the source two observational methods were used: cross-scanning and mapping. In total, radio flux densities of 192 galaxies have been derived (Niklas et al., 1995). Additionally, a literature search was made in order to get flux densities at other frequencies.

This southern galaxy with its fairly regular pattern is well suited to study the influence of a bar onto the magnetic field in a galaxy. With its low inclination of 24° it provides a geometry similar to M 51. Also the magnetic field strength of 11 ± 2 μG is in the same range.

Theoretical arguments provided the first definitive prediction for the existence of an interstellar magnetic field in our Galaxy: There was no other way to explain the observed isotropy of the cosmic radiation. Alfven, Richtmeyer and Teller (1949), and Fermi (1949) stated that the particles of the cosmic radiation have to be reflected often and this can hardly be explained other than by an interaction with a magnetic field.

Ringlike structures (in H α, CO and radio continuum) in central galactic regions have been observed in a number of objects. They seem to be a basic feature of galactic structure (for references see Dickman et al., 1988). These observations can be summarized as follows: The typical mass of these rings is 108 – 109 M ⊙. The gas distribution is smoothly decreasing from the ring into the innermost galactic regions. The rings appear always at the turnover radius where the galactic rotation turns from rigid to differential rotation.

Continuum observations of the southern extension of the radio Arc located near 1~0.2° have been carried out at λ20 and 6cm using the VLA in its hybrid B/C and C/D array configurations. A number of long and narrow filaments have been identified on the negative latitude side of the plane. Some of the filaments appear to extend continuously into the radio continuum Arc and suggesting strongly that they are associated physically with the Arc. Other filaments appear isolated and thus have characteristics similar to those of the radio “threads” which have been seen near the Galactic center. These new threads and filaments are highly polarized at λ6cm and show rotation measures which vary between 300 and 3000 rad m−2. The details present in the high-resolution images of this region strengthen the hypotheses that the large field strength is dynamically important and that the large-scale geometry of the magnetic field is poloidal near the Galactic center.

We have begun a long-range project to study southern galaxies using the radio telescopes at Parkes and Molonglo, the Siding Spring optical facilities and soon, the Australia Telescope. Here we present the results of polarization mapping at two wavelengths of the galaxies NGC 55, 253,4945, M 83 and the Circinus Galaxy.

High-resolution, high-sensitivity observations of the CO(J=2-1) lines in the galaxy M82 have revealed that the rotation of the gas disk is Keplerian, which suggests that the galaxy has no massive halo. The extended molecular gas halo, extending up to ±2 kpc above the galactic plane, shows very slow rotation and indicates that the halo gas has been ejected from the central region in angular momentum conservation

We discuss the origin of the observed strong poloidal fields Bz in the central regions of galaxies which have gaseous rings. In the context of galactic disk dynamo models only weak poloidal fields but strong toroidal fields result (Bϕ > Bz). Therefore we tie the strength of the poloidal fields to the central activity and apply known and tested ideas rigorously. A battery process on galactic scales is discussed which ensures the existence of a large scale magnetic field in the inner galactic region. The frozen-in field may be amplified by compression and turbulent stretching; the resulting field is poloidal. The central activity provides a nonaxisymmetric flow field which, just as the α – ω dynamo produces mostly Bϕ > Bz, can produce Bz ≥ Bϕ. This model explains the structure and strength of the magnetic field in star-burst galaxies like M82 (Lesch et al., 1989).

On presente les techniques d'observations, les donnees d'observations courantes et les methodes utilisees pour obtenir la configuration du champ dans les galaxies spirales. On discute de la configuration du champ et de ses implications sur la dynamique, l'evolution et l'activite dans les galaxies spirales

Seven new pulsars are reported from the Molonglo radio observatory. Some conclusions can be drawn about the distribution of pulsars in the galaxy.

The 100-m fully steerable radio telescope of the Max-Planck-Institut fur Radioastronomie (MPIfR) has now been in service for over a year. The telescope was designed to allow observations in the decimeter and centimeter wavelength regions, with the vastly improved resolution given by the 100-m diameter. During construction of the telescope measurements were made at a wavelength of 75 cm. Since the completion of the adjustments, tests and observations were made at 11-cm and 2.8-cm wavelengths. In particular, at the 2.8-cm wavelength, tests have fully confirmed the design goals. In fact, we hope to extend the operational range of the telescope at least to the wavelength of 1.2 cm. A number of problems, new in this field, had to be solved in the construction of an instrument of this size and precision. Measuring methods are described which allowed adjustment of the surface to ±1 mm. A computer-controlled servo loop allows setting of the telescope to 5". Experience of operation under various conditions is described.

The highest frequency at which a radiotelescope can be used depends on the surface accuracy. The rms error of the surface should be less then l/16th of the shortest wavelength. This should be not only under static conditions but also when the telescope is being driven, under the influence of wind and temperature changes. With this in mind we can trace back the development of the paraboloidal dish since the time when Grote Reber constructed his antenna in Wheaton, Illinois.

The accuracy of the absolute value of solar flux depends on the temperature calibration techniques and the knowledge of the gain of the aerial used for the measurements. Recent advances in low-noise receivers, microwave components, and amplifier stability have reduced considerably the errors due to temperature calibration techniques. At present the knowledge of the gain of the aerial used for calibrations (usually a pyramidal horn) presents the largest source of doubt of an absolute calibration. Investigations of this problem suggest that a ‘standard gain horn’ should be employed at all observatories in absolute solar calibrations.

The pulsed radio sources1,2 emit energy almost simultaneously over a wide frequency band3. Pulses from the source at 19h 19m 37s, + 21°47′02″ (epoch 1950) have been received with the Australian 210 ft telescope at frequencies of 85, 150, 630, 1,410 and 2,700 MHz. This report covers measurements of the spectrum of the pulses, the characteristics of the intensity variations at different frequencies, and observations of the structure and polarization of the pulses. A previous communication4 discussed measurements of the period of the pulses and of the dispersion between 85 and 1,410 MHz.

A large project of studying various transitions and isotopic species of CO in M82 has been carried out with the 30-m IRAM radio telescope. A l!6x1!0 area was mapped in 12CO(2→1) with 13″ resolution (Loiseau et al., 1988a). The purpose of these observations was to obtain high signal-to-noise, high resolution data for comparison with the 12CO(1→0) observations of Nakai et al. (1987). A 13CO(2→1) observation covered the central 1!0x0!7 region (Loiseau et al., 1988b) and allowed to establish the velocity field of CO in the inner nuclear region. The position angle of the rotation axis of 13CO is aligned with the optical rotation and at some 30° relative to the 12CO velocity field. The 13CO map also shows the existence of clumped emission in the central region.

The outstanding feature of the last triennium was most certainly the abrupt generalisation of the use of array detectors, particularly CCDs (charge coupled devices). The latter pervade all subdivisions of instrumental astronomy. The gains achieved by their high quantum efficiency, their stability, their capability of delivering immediately recordable signals which can be processed by appropriate computational means, have been the cause of spectacular progress regarding the photometric precision of weak signal measurements.

The existence of ‘haloes’ in clusters of galaxies was deduced by Ryle and Windram (1968) for the Perseus cluster and by Willson (1970) for the Coma cluster at 408 MHz by comparing total flux measured by a single dish with the sum of fluxes of radio sources found in the field. A direct measurement of the extended source Coma C was made by Jaffe et al. (1976) at 610 MHz. The failure to detect the halo of Coma at higher frequencies is attributed by all authors to a steep spectrum of this extended component.

Publisher Summary This chapter discusses the basic concepts related to antenna calibration. Direct antenna calibrations of radio telescopes—such as the measurement of the polar pattern on a turntable—are usually not possible. Present-day radio telescopes are too large for these methods, which are generally employed in the testing of antennas for radio communication purposes. To achieve meaningful calibration by scaling, both a far-field measurement of the polar pattern of the model and near-field probing of the aperture field in the model and of the full antenna need to be combined. Consequently, very specialized and intricate measurements must be made before a successful antenna calibration is available. The criteria for the selection of calibration sources are described in the chapter, and lists of calibrators, both for positional and for flux scale calibration, are given. With a view of the discrepancies between observatories at frequencies of 408 MHz and below, discussion of present-day accuracy of the flux scale is undertaken. The techniques of calibration are described, as used in the tests of the 100-m fully steerable, paraboloidal radio telescope at Effelsberg. A description of the aims of a complete pointing theory is also presented.

Global configuration of magnetic field in several spiral galaxies were determined by analysing characteristic variation of Faraday rotation within the galaxy disks. The majority has an open spiral, bisymmetric field configuration, while some (10–20%) have a ring field.

Total-power and polarization observations of NGC 253 at 10.7 GHz have been performed with the 100-m MPIfR radio telescope. The observed arm/interarm polarization contrasts are discussed in the context of possible field configurations in spiral arms.

A NEW series of observations of the galactic radio emission has been conducted at the frequencies of 20, 30 and 85 Mc/s. These low-resolution observations made with scaled aerials were intended to investigate the spectral index of the galactic radio emission in the frequency region 10–100 Mc/s.

High-resolution surveys of the galactic radio emission show detailed structure both near the galactic plane and at high galactic latitudes. Some of this structure is describable as ‘spurs’ while the rest comprises isolated features. We describe here measurements of the spectral index of the background radiation with a resolution of 3°.5. These measurements are aimed at a detailed understanding of the high-latitude synchrotron emission.

KNOWLEDGE of the intensity–frequency relation of extraterrestrial radio emission has been obtained from scaled aerial experiments at frequencies higher than 20 Mc/s (refs. 1 and 2) and from ground-based or satellite-borne radiometers operating below 10 Mc/s (refs. 3, 4 and 5). The low-frequency observations, whether ground-based or satellite-borne, are affected by the ionosphere. The consequence of these ionospheric effects has resulted in difficulties being experienced when reconciling the observations in frequency regions below 10 Mc/s with those above 20 Mc/s.

Pulsars display a complicated pattern of amplitude variations. The scale of variations range from months through hours to sub-milliseconds. The purpose of this note is to present polarization data for CP 1919 and intensity distribution data for PSR 0833—45 which are relevant to pulse-to-pulse variations and the variation over periods of hours respectively.

FOUR further pulsars have been discovered at the Molonglo radio observatory during a pulsar search at 408 MHz. One of the four pulsars, MP 0254, a high galactic latitude pulsar, was discovered in November 1968, but failed to appear on any of some twenty subsequent transits. In a recent observing session this pulsar was observed twice, allowing measurement of the dispersion and pulse width. Two of the pulsars (MP 1706 and MP 1911) were among many suspected pulsars noted during a close re-examination of the search records made since October 1968 using the two beam technique which led to the discovery of eighteen pulsars1–4. Recent observations have confirmed the existence of MP 1706 and MP 1911, and have enabled their properties to be measured. The fourth pulsar, MP 1154, was discovered during a search for high dispersion pulsars along the galactic plane using a two channel dispersion remover which was described in connexion with the discovery of MP 1240 (ref. 3).

THE pulsar CP 1919 (ref. 1) was observed at Parkes2 in March 1968 at a number of radio frequencies. On occasions the frequencies 85, 150, 150.9, 630 and 1,410 MHz were used simultaneously, with the 210 foot telescope tracking the source for some 4 h. The data have now been examined for statistical occurrence properties and a quantitative description of the source can be given. The statistics of pulse occurrence are of general interest because theories of emission (and pulse propagation) require these data. And anyway an observatory embarking on a programme of searching for such objects must know the statistical properties of pulse occurrence to aid in determining an observational programme.

WE recently described1 the discovery of seven pulsars found in a search at the Molonglo Radio Observatory using the 408 MHz radio telescope. A conclusion reached on the basis of this search was that pulsars are galactic objects associated with the disk or the spiral arms, but with a somewhat anomalous distribution. A zone of avoidance along the inner regions of the galactic plane was suggested, based on the argument that dispersion in the thin layer of an ionized medium closely confined to the galactic plane results in the loss of the distant pulsars. This communication describes the discovery of further pulsars which follow the same general pattern of galactic distribution.