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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.

The observation of an area of 120° × 56° centered on RA=8h DEC=20° at 408 MHz was the first astronomical use of the MPIfR 100-m telescope (1970) and was designed to compile a complete sky survey using also data from Jodrell Bank and Parkes (Haslam et al., 1982). The observation of the northern sky at 1420 MHz started in 1972 using the Stockert 25-m telescope and was finished in 1976 (Reich and Reich 1986). This survey has been completed to an all sky survey using data from Villa Elisa (Argentina). The two surveys are absolutely calibrated. The angular resolutions are 0.8° and 0.59°, respectively. A number of surveys of the Galactic plane have been made with the 100-m telescope at arc minute angular resolution. Surveys at 2695 MHz (|b| ≤ 5°) (Reich et al. 1990, Fürst et al. 1990) and at 1410 MHz (|b| < 4°) (Reich et al. 1990) are public.At medium Galactic latitudes (up to |b| = 20°) the emission consists mainly of faint extended ridges or arcs superimposed on the still dominating, about 10 times stronger, diffuse Galactic emission. They have never been investigated in a systematic way although they provide important clues for the understanding of the “disk-halo connection”. This region is covered by new observations at 1400 MHz with the 100-m telescope.

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.

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.By applying our newly developed polarization CLEANing technique we are able to diminish instrumental polarization effects. Since Faraday rotation is negligible at λ2.8 cm the measured linear polarization is a direct trace of the projected magnetic field in Vir A. In combination with low-frequency data obtained with the VLA it is possible to determine parameters like spectral indices, break frequencies, and spectral ages.

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.

The rotation velocity of molecular gas in the halos of M82 and NGC4631 decreases with the height from the galactic plane. The slower rotation of halo gas can be explained if the gas is supplied from the central region of the galaxies due to some ejection.

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.

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).

Radio continuum surveys give us the fundamental information about the distribution of the radio intensity across the sky. The radio waves originate in three fundamental emitting processes and are measured superposed in the antenna beam. At the lowest radio frequencies (below 10 GHz) the nonthermal emission process (synchrotron radiation) predominates. This radio emission comes from supernova remnants, from the “galactic background” (relativistic electrons diffusing in galactic magnetic fields), but also from extragalactic objects (galaxies, quasars, radio galaxies, etc.). In the frequency range 10 GHz < f < 300 GHz the thermal (free-free) process becomes dominant. In the Galaxy we see the HII regions along the galactic plane. In nearby galaxies we can identify the thermal emission in the disks. Above 300 GHz the dust is seen. This is the boundary region between radio and far-infrared radiation.

Radio galaxies are known to exhibit a variety of scales in their structure. First we have the nuclear sources, which so far have not been completely resolved even on the scale of 1/10 milliarcsecond with VLBI observing methods (e.g. Preuss, 1981). Then we have the ‘jets’ (which at some stage break up into ‘blobs’) which are considered to transfer energy from the ‘nuclear engine’ to the outer heads. The latter appear to be the sites of transfer of the collimated jet energy into a diffuse emission region. Despite their usually low brightness these diffuse emission regions dominate the internal energy content in particles and fields, even for the collimated doubles. Note that only 1% of the total energy in Cyg A is in the hot spots (Perola, 1981).

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.

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.

The four clumpy irregular galaxies Mkr 8, 296,297 and 325 have been observed by IRAS. All galaxies have been detected in at least two of the four detector bands. The ratios of the 100 to 60-m flux densities are comparable to those of HII regions or violently star forming galaxies. The average star formation rate in clumpy irregular galaxies is of the order of a few solar masses per year (based on their average far-infrared luminosity and a Hubble constant of 75 km s−1 Mpc−1.

In the framework of the diffusive shock acceleration of relativistic electrons in extragalactic jets, we show that it is possible to derive the speed of the jet. For this purpose, we transform continuity relations through an oblique shock front into the reference frame of the observer. We apply these calculations to knot A of the M87 jet. Measuring the deviation of the fluid through the shock front from high-resolution radio maps and the deviation of the magnetic field from optical polarization maps (Fraix-Burnet et al., 1989), we derive speeds of about 0.01 c (Fraix-Burnet and Biermann, in preparation). The compression ratio is most probably 4 and the magnetic field is nearly parallel to the shock front both upstream and downstream.