The problem of the nuclei of galaxies is really one of the most important problems on the way to our understanding of numerous very strange phenomena which we observe in our own Galaxy as well as in many others, especially in radio galaxies.

The work reported on was done by G. W. Rougoor and is based on observations made with the Dwingeloo dish and the eight-channel receiver built by Professor Muller.

The 21-cm hydrogen radiation near the galactic plane exhibits strong deviation from circular motion over longitudes within 30° or so of the galactic centre. In order to extend the observations first made by Rougoor and Oort,* the Carnegie multichannel H-line spectrograph was used with our 60-foot radio telescope at Derwood, Maryland, in order to confirm the Leiden work and extend observations to more southern longitudes. Cross-sections extending ±2° in latitude were taken every 2° in longitude from lII=−26°8 to lII=+2°2 and a series of points along the galactic equator were taken every 1° over the same range. Effort has been concentrated on the southern extension of the observations, which agree well with the Leiden observations over the section in common, but which carry the observations nearly 20° farther south in longitude.

A detailed study of the galactic centre region is being made with the 210-foot telescope at Parkes and a 48-channel hydrogen-line receiver. Line profiles have been recorded on a 6-min-of-arc grid over a central area 2° square, and also along the galactic equator and a number of other longitude lines. These observations, which have been partially reduced, show that the structure and motions of the gas are very complex in the neighbourhood of the centre.

The large Pulkovo radio telescope has a beamwidth of 7 min of arc in R.A. at a frequency of 1420 Mc/s. The continuum emission from the source Sagittarius A was measured with a bandwidth of 5 Mc/s. The mean drift curve is shown in Figure 1. It can be separated into components according to Drake (1959) as indicated in the figure. The galactic ridge is also shown. The right ascension, the antenna temperature, the observed angular diameter, and the flux density of each component are given in Table 1. The errors given in the table can be somewhat higher in the case of components 2 and 3 because of the difficulties of separating them. The calibration of the antenna and receiver was made using the flux densities of the sources IAU 19N4A, 05N2A, 05S0A, and 18S1A according to Westerhout (1958) with the corrections given by Altenhoff et al. (1960). The atmospheric extinction at λ = 21 cm was taken from these works as well.

I. The large positive and negative velocities in the 21-cm line profiles near the galactic centre have indicated the presence of substantial departures from circular motions in the central parts of the Galaxy. The Leiden astronomers (Oort and Rougoor 1958; Rougoor and Oort 1960) have interpreted these observations in terms of an “expanding arm” at a mean distance of about 3 kpc from the centre. It is not clear how these arms or arcs are related to the regular spiral structure, if the Galaxy is an ordinary spiral similar to M31 as commonly assumed. If, on the other hand, the Galaxy is similar to the SAB(r) or SAB(rs) systems, as suggested by the multiplicity of the spiral pattern discussed in another communication, a different interpretation of the velocity distribution is possible.

La Station Française de Zeekoegat (Province du Cap—Afrique du Sud), construite dans le cadre de l'Observatoire Européen Austral est consacrée à l'étude des vitesses radiales par le prisme objectif de Fehrenbach. Parallèlement aux observations du prisme objectif, nous avons, avec P. Cruvellier, conduit un programme d'observations des régions HII de l'Hémisphère Sud.

In the present paper we shall consider that the HII complexes observed in galaxies may be interpreted as the resulting Strömgren volume produced by a cluster or association of exciting stars. If ρH is the density of the hydrogen surrounding the cluster or association and I the number of ionizing quanta (λ < 912 å) emitted by the stars, the ionized volume becomes

The original plans for this Symposium called for a review of galactic problems by the late Dr. J. L. Pawsey and myself. In the early days of radio astronomy Pawsey often represented CSIRO at international symposia. Many of us enjoyed the lucid reviews that he presented of the work done at CSIRO, much of which was carried out under his inspiring and energetic guidance. It is at a moment such as the present one that we remember him vividly and miss him deeply.

In order to introduce this Symposium on the Magellanic Clouds I feel the most valuable thing I can do is to discuss our understanding of galaxies in general, then show how the Magellanic Clouds in particular fit into the sequence of galactic forms, and finally note a few of the critical problems of galaxies which we might solve by studying the Magellanic Clouds. There are six main points which I wish to mention.

La méthode de mesure des vitesses radiales au prisme objectif à champ normal que nous employons à l'Observatoire de Haute Provence depuis de nombreuses années (Fehrenbach 1947, 1948, 1955) est la méthode idéale pour la recherche des étoiles de grande luminosité, membres des Grand et Petit Nuages de Magellan.

The material which I wish to present today is set out in Royal Observatory Bulletin Number 66, of which I have a few advance copies with me. The paper describes measures of about 700 stars in an area about 1° square. These are nearly all the stars down to a limit of V =14m5 in the area. Proper motions were measured by comparison between two plates taken on 1912 Jan. 21 and 1960 Nov. 16–17. The earlier plate had an exposure of 5 hr, which is exceptionally long for astrographic plates of those times. The measures of Ax and Ay (the shifts in units of one-tenth of a micron in the directions of right ascension and declination) were reduced by constructing plate constants such as would make the least-squares motion of the stars with B – V < 0 zero. In the reduction 104 such stars were used. The standard errors of measurement are σ(x) = ±15·9 and σ(y) = ±14·9, assuming that these stars really are members of the LMC and exhibit no relative proper motion. By using these plate constants, values of Ax and Ay were computed for all the remaining stars. The stars with 0·5 < B – V < 1·5 (apart from cepheids and a few reddened stars) are very plainly shown by their proper motions to be nearly all field stars, and indeed their motions can be satisfactorily explained by supposing them to be galactic stars showing the parallactic motion, galactic rotation, and a velocity ellipse appropriate to galactic stars. Stars with B – V > 1 · 5 cannot be determined to be members of the LMC on proper motion alone, but other considerations suggest that this is so. For example, their x, y distribution in the field follows the same pattern as that shown by the very blue stars, whereas the field stars (0 · 5 < B – V < 1 · 5) are uniformly distributed over the plate.

Some years ago the plates used for the extended Uppsala–Mount Stromlo Atlas of the Magellanic Clouds were searched for clusters in order to compare the optical extension of the Large Cloud with the one defined by the radio-astronomical observations of neutral hydrogen. Slightly over 150 clusters were identified and good agreement between the radio and optical boundaries was noted (Westerlund, unpublished data).

Before discussing the results of the radio observations of the Magellanic Clouds in detail, it is worth while to briefly review some of our current ideas about radio emission from “normal” galaxies which would be the classification given to the Clouds by radio astronomers. A “normal” galaxy has no striking visual peculiarity and has a much lower ratio of radio to light flux than the “radio” galaxy.

Earlier surveys of the line radiation from neutral hydrogen in the Magellanic Clouds (Kerr, Hindman, and Robinson 1954; Hindman, Kerr, and McGee 1963; Hindman et al. 1963) have shown that the amount of gas associated with these extragalactic bodies is relatively large. The gas appears widespread, surrounding the stellar bodies in a single continuous and very tenuous envelope with a marked bridge in the vicinity of the optical wing of the SMC linking the two main concentrations.

Some while ago radial velocities were published for 112 stars in both Magellanic Clouds from Radcliffe Cassegrain spectrograms (Feast, Thackeray, and Wesselink 1960).

The rotation curves of the LMC and the Galaxy differ markedly by the slope of the curve near the centre. Two causes may be responsible for this difference. Firstly, the mass of the Galaxy exceeds that of LMC by about one order of magnitude and the resulting orbital velocities at corresponding distances must be larger in the Galaxy than in the LMC. Secondly, the distribution of mass may be different in the two systems. Indeed, several investigations showed that the Galaxy is best represented by a model exhibiting a strong concentration of mass while the LMC is consistent with models of a very weak concentration, a homogeneous spheroid yielding a passable approximation.

I. The main structural characteristics of the irregular barred spirals of the magellanic type are illustrated in Figure 1. They were first detected 10 years ago on small-scale photographs of the Large Cloud taken at Mount Stromlo (de Vaucouleurs 1954, 1955) and were later found to be uniformly present in many other “late-type” barred spirals designated SB(s)d and SB(s)m in the revised classification system (de Vaucouleurs 1959). These stages form a continuous transition between the regular barred spirals of the “S-shaped” sequences, such as NGC 1365: SB(s)b, NGC 1300: SB(s)bc, NGC 7479: SB(s)c, and the completely irregular system IBm showing only an axial bar and little or no traces of whorls, such as NGC 4449 and 4214. Examples of the transition stages are NGC 7741: SB(s)cd, NGC 1313: SB(s)d, NGC 4027: SB(s)dm, NGC 4618: SB(rs)m, and the Large Magellanic Cloud: SB(s)m (Fig. 2). The Small Cloud, because of its interaction with the Large Cloud and its unfavourable inclination, is more difficult to classify precisely; it may be designated as SB(s)mp or IB(s)mp to indicate the presence of residual (or incipient) spiral structure (de Vaucouleurs 1957a).

Twenty-one-cm neutral hydrogen emission from NGC 55 has been measured with the 210-foot radio telescope at Parkes and a low-noise receiver (Robinson 1963). The beamwidth at 21 cm is 13′.5. NGC 55 has been classified by de Vaucouleurs as a SB(s)m system similar to the LMC, seen edgewise and with the luminous bar nearly along the line of sight (de Vaucouleurs 1961). The outer isophote published by de Vaucouleurs has dimensions of 45 by 9′, centred about 2′.5 to the south-following side of the bright “nucleus” in the centre of the bar.