Maffei 2 is a highly obscured galaxy, probably of type Sbc, at a distance of 5 Mpc (Allen and Raimond 1972; Spinrad et al. 1973). Since it lies close to the Galactic plane, there is considerable confusion in infrared and 21-cm HI observations due to Galactic emission, but investigations of its structure can be carried out at millimeter wavelengths where the Galaxy contribution is confined to a limited velocity range. The high resolution (30″) of our CO J=2–1 observations permits both a detailed examination of Maffei 2 and a study of the nature of the gas in its nucleus, through comparison with the CO J=1–0 observations.

When the Columbia Southern Millimeter-Wave Telescope on Cerro Tololo, Chile, began operation in January 1983, one of the main goals was to make the first extensive out-of-plane survey of 2.6-mm CO emission in the Southern Milky Way. Because this telescope, a 1.2-meter Cassegrain, is a close copy of the Columbia telescope in New York – with nearly identical antenna, feed, and calibration – it will be very easy to join our northern and southern surveys to make the first homogeneous radio survey of the entire Galaxy. The Chile telescope does have one important improvement over the New York system: a liquid-nitrogen-cooled receiver with a single-sideband noise temperature of 385 K. Details of the telescope are given in Cohen (1983).

The southern galactic-plane region, in the ranges 294° ≤ 1 ≤ 358°, −0°.075 ≤ b ≤ 0°.075, has been surveyed in the J = 1–0 line of 12CO with a sampling interval of 3′ arc. Observations were made with the 4-metre telescope at the CSIRO Division of Radiophysics in 1980 and 1981. Details of equipment and observing procedure are given in Robinson et al. (1982, 1983); see also McCutcheon et al. (1983).

We have used the Estec/Utrecht heterodyne submillimetre receiver together with the 1.4 m ESO CAT at La Silla (Chile) to survey the southern Galaxy (1 = 270 − 355°) in the CO(2–1) transition at 230 GHz (1.3 mm). The beam used had a HPBW size of 5.5 arcmin, overall system efficiency was 0.35, and the system temperature was 1400 – 1750 K (DSB). Our filterbanks had velocity resolutions of 1.3 and 0.325 km s−1 and velocity ranges of 333 and 83 km s−1 respectively.

The latitude distribution of the emission from the 12CO J=1→0 rotational transition has been surveyed for the region 350° ≤ 1 ≤ 25° at b = 0′, ±10′ and ±20′. Most of the 12CO emission in the inner Galaxy, the region extending from the galactic center to 4 kpc radius, is produced by three large and massive objects: the nuclear disk/bar, the 3-kpc arm and the “+135 km s-1 feature”. These structures all have observed HI counterparts and each shows extremely large deviations (50–180 km s-1) from circular motion. Observations of 13CO in selected directions show that the two structures outside the nuclear disk each span at least 2 kpc in length and that together they imply ≥ 1055 ergs in kinetic energy of expansion away from the galactic nucleus.

Since our original report of CO emission from outside the solar circle in the first quadrant (Kutner and Mead, 1981) we have extended the observations in two ways: (1) We have improved latitude and longitude coverage. Preliminary results on the latitude distribution were reported by Kutner (1983). (2) We have extended our cloud mapping, giving us at least partial CO maps of 55 clouds, along with 13CO, C18O, CO (2–1), and 2-mm H2CO observations of some clouds.

The distribution of CH in the Galaxy has been investigated via its main-line transition in the 2Π1/2, J=1/2 ground-state Λ-doublet at 3335 MHz. The galactic plane was observed with a spacing between adjacent points of 2°.5 in the longitude ranges 10°-60° and 310°-350°. The northern data (Johansson, 1979) were obtained with the 25.6-m telescope of the Onsala Space Observatory and the southern data with the Parkes 64-m antenna; the corresponding beamwidths are 15′ and , respectively.

The COS-B gamma-ray survey is compared with 12CO and HI surveys in a region containing the Orion complex and in the outer Galaxy. The observed gamma-ray intensities in the Orion region (100 MeV<E<5 GeV) can be ascribed to the interaction of uniformly distributed cosmic rays with the interstellar gas. Calibration of the ratio between H2 column-density and integrated CO line intensity resulted in the value: (3.0±0.7)x102 0 molecules cm-2K -1km -1s. In the outer Galaxy HI column-density maps in three galacto-centric distance ranges are used in combination with COS-B gamma-ray data to determine the radial distribution of the gamma-ray emissivity. A steep negative gradient of the emissivity for the 70 MeV-150 MeV range and an approximately constant (within ~20%) emissivity for the 300 MeV-5 GeV range is found. The result is interpreted as a strong decrease in the cosmic-ray electron density and a near constancy of the nuclear component.

The Infrared Astronomical Satellite (IRAS), launched 1983 January 25, has been conducting a high-sensitivity, high-resolution all-sky photometric survey at wavelengths of 12, 25, 60, and 100 μm in the infrared. One of the data products from the survey will be a map of the entire Milky Way within latitude limits of 10 degrees at a resolution of 4 arcminutes. Since the IRAS detector system is DC-coupled and has demonstrated excellent stability, this map will contain reliable information on all spatial scales larger than the map resolution. The extremely high sensitivity of the IRAS instrument for the detection of interstellar material in the survey mode is illustrated here in terms of visual extinction and dust and gas column densities.

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :

a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).

b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).

c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).

During its 6.7-year lifetime the COS-B experiment included about 15 months of observations towards latitudes |b|> 20° and covered almost all latitudes from the South to North galactic poles. Studies comparing the local gamma-ray emission with the distribution of gas (Lebrun et al. 1982, Strong et al. 1982) have so far been limited to 10°<|b|< 20°, where the correlation is found to be fairly good and the structured emission can therefore be attributed mainly to cosmic-ray interactions with gas. The extension of this type of analysis to higher latitudes is now possible using the COS-B database.

Observations of the far-UV spectrum (1300–1800 å) of the sky background at different galactic latitudes are presented. The measurements were made in deep space, at distances up to 2 × 105 km from the Earth with the photoelectric spectrometer (“Galaktika”) on board the “Prognoz-6” satellite. The highly elongated orbit of the satellite permitted corrections for scattered Lα-light. The contribution of stars was eliminated using fluxes measured in the TD-I and OAO-2 experiments.

The radio continuum emission of the Milky Way and nearby galaxies can be decomposed into a central region, a clumpy “thin disk”, concentrated in the spiral arms, and a smooth “thick disk” (or flattened “halo”). The emissivity ratio of the two disks seems to be related to the magnetic field properties: Galaxies with strong radio spiral arms reveal a highly ordered field following the arm direction, while galaxies with diffuse disks contain a less ordered, smoothly distributed field. The degree of uniformity of the field seems to correlate with the total optical luminosity. The average magnetic field in the Milky Way is weak and turbulent compared to most of the nearby galaxies observed so far.

The distribution of total spectral indices between 38 and 408 MHz with a resolution of for δ>-25° has the following main properties:

1. Relatively small variations of spectral indices over the sky.

2. High indices in the central region at high galactic latitudes.

3. Moderately low spectral indices in the anticentre region.

4. Lower indices in the low-brightness regions (cold holes).

5. The lowest indices in regions containing large amounts of HII.

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 distribution of Faraday rotation measure (RM) of extragalactic radio sources shows that a large-scale magnetic field in the Galaxy is oriented along the spiral arms. The field lines change direction from one arm to the next in the inter-arm region.

The spiral structure of the Milky Way galaxy has always been somewhat elusive because of our internal vantage point. This review will present methods and data for determining the overall pattern, and will summarize various models that have been proposed. Observations of spirals in external galaxies will also be discussed, because they can provide insight into the spiral structure of the Milky Way.

We analyse the distribution of peculiar velocities of stars within 200 pc of the Sun in terms of space variations of the velocity ellipsoid.

Compression of the interstellar gas by a passing density-wave is thought to be responsible for triggering the presently observable star formation processes in the arms of spiral galaxies. We present new observations of the distribution and kinematics of the Hβ emission in the spiral arms of M83, obtained with the TAURUS imaging Fabry-Pérot system. These results, when combined with observations of the neutral and molecular components with sufficiently high resolution, should contribute to our understanding of the time sequence by which stars form out of the interstellar gas.