This introduction reviews early observations of the Magellanic Clouds, briefly describes the “Golden Age of Magellanic Discoveries”, and looks ahead at promises for dramatic new results from the powerful telescopes of the 21st century.

We use observations and evolutionary models of local objects to interpret a recent determination of the star-formation history of the universe. By fitting the global star-formation rate, the model predicts the ratio of spheroid to disk mass of ~1, an intergalactic medium (IGM) whose mass is ~2.3 times the mass in stars, and whose metallicity is ~0.1 Z⊙.

What's in a name? Everything! SMC 1 is a planetary nebula in the Large Magellanic Cloud! URLs of Web documents are given to aid astronomers in designating their astronomical sources so as to avoid confusion in the literature.

Novel instrumentation has always led to new insights in the nature of the universe. Novel astronomical instrumentation is no exception. In numerous areas new instruments led to the detection of hitherto unknown phenomena. I will review some notable studies of the recent past with some emphasis on those dicoveries not extensively covered by others at this conference. Finally, very recent work based on ORFEUS echelle spectra is presented.

The Magellanic Clouds are unique in providing sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) all the way up to global scales. We present a sample of recent and current work using the MCELS dataset.

The Large Magellanic Cloud contains an extensive distribution of hot plasma and is one of the brightest extragalactic regions in the diffuse 0.5–2.0 keV X-ray sky. The plasma is not isothermal but increases in color temperature from west to east from ~106.6 K to ~106.9 K. The total flux from this plasma is ~ 1038 ergs s−1. The average emission measure is ~ 0.014 cm−6 pc, which if the emitting plasma is distributed uniformly throughout the LMC, implies a space density of ne ~ 0.002 cm−3. There is an apparent ¼ keV enhancement in the southwest of the LMC, which if associated with the LMC implies a considerable emission measure of ~ 106 K plasma. (The foreground column density of Galactic neutral hydrogen is ~ 6 × 1020 cm−2, or several optical depths for ¼ keV emission.)

The Small Magellanic Cloud exhibits less diffuse X-ray emission in the 0.5–2.0 keV band than the LMC with a total flux of ~ 4 × 1036 ergs s−1. The average emission measure of ~ 0.006 cm−6 pc also implies a space density of ne ~ 0.002 cm−3. The optical depth of Galactic HI for ¼ keV X-rays from the SMC is considerably lower than that for the LMC. However, while there is a significant variation in the ¼ keV band intensity over the SMC field, it is in general not particularly well correlated with anything associated with the SMC, although there is an enhancement which may be related to the leading edge of the SMC. Considerably more work is needed to unravel the origin of the structure, which may be associated instead with either emission or absorption variations in either the disk or halo of the Milky Way.

We review observations of neutral atomic hydrogen (HI) in the Magellanic Clouds (MCs). Being the nearest gas-rich neighbours of the Milky Way the MCs give us an excellent opportunity to study in detail the structure and evolution of the interstellar medium (ISM) and the effect of interactions between galaxies. HI in emission provides a probe of the structure and velocity field of the Clouds, allowing the study of their velocity dispersion, 3-D structure, and large-scale total-mass distribution. Recent data from Australia Telescope Compact Array surveys reveal a morphology (for both Clouds) which is heavily dominated by the effects of local star-formation, rotational shear, fragmentation, self-gravity and turbulence. The new data, which has a spatial resolution down to 10 pc, also allows the study of the distribution functions in velocity and mass for HI clouds. We discuss the morphology, dynamics and giant shell population of the LMC and SMC.

Surveys of λ21-cm absorption in the Magellanic System show that the cool phase of the HI is less abundant in the SMC than in the Milky Way, and may be so also in the LMC. The typical cool cloud temperature is colder than in the Milky Way, 30 to 40 K rather than 60 to 75 K. The lower abundance of cool phase HI can be traced to the lower heavy element abundances in the Magellanic environment. The cooler cloud temperatures are somewhat mysterious.

The first results from the HI Parkes All-Sky Survey (HIPASS) provide a spectacular view of the global HI distribution in the vicinity of the Magellanic Clouds and the southern Milky Way. A 2400 square degree mosaic around the South Celestial Pole (SCP) reveals the existence of a narrow, continuous counter-stream which “leads” the direction of motion of the Clouds, i.e., opposite in direction to the Stream. This strongly supports the gravitational model for the Stream in which the leading and trailing streams are tidally torn from the body of the Magellanic Clouds. The data also reveal additional tidal features in the Bridge region which appear to emanate from the LMC, and a distinct spiral structure within the LMC itself.

Observations of interstellar C IV toward six stars in the Large Magellanic Cloud are described. These data were obtained with the GHRS on HST and with IUE. They provide the first unambiguous evidence that C+3 exists in the Large Magellanic Cloud away from regions where it could have been produced locally, as the six stars are of spectral type later than 08, as well as away from hot early-type stars or active regions. Significant differences between the velocities of the C+3 absorption and those of Hα emission near the stars shows that these ions are not co-spatial, implying that the C+3 originates in the halo of the LMC. It is shown that photo-ionization is unlikely to be the sole source of the C+3 and that the LMC halo thus contains hot gas.

We have made a 12CO(J = 1−0) survey of the LMC with NANTEN. A sample of 55 giant molecular clouds has been identified and comparisons with stellar clusters, HII regions and SNRs are presented. The connection between the clouds and cluster formation is discussed.

The molecular gas content in the Magellanic Clouds has been studied, with different spatial coverage and resolution, through obervations of CO(1-0) line emission. In the LMC and the SMC the molecular gas is dominated by clouds whose properties are different from those of their Galactic counterparts. The relation between the intensity of CO emission and molecular hydrogen column density, or the conversion factor X, is different than that of molecular clouds in our Galaxy and depends on the ambient physical conditions. Studying the molecular gas through observations in the H2 emission line may prove an alternative way to determine the molecular content associated with star forming regions in the Magellanic Clouds. In particular, results obtained towards 30 Doradus in the LMC are presented.

Over the past decade, substantial progress has been made in understanding the properties of Magellanic Cloud supernova remnants and their role in the ISM. Among the notable results are the “typing” of progenitors via the X-ray spectra of their remnants, the use of X-ray spectra to measure ISM abundances, and the discovery of remnants with unique properties. I summarize recent studies of MC SNRs, and describe how a refined understanding of the SNR population requires consideration of the unique attributes of each remnant.

Superbubbles that result from the stellar winds and supernovae of OB associations probably play a fundamental role in the structure and energetics of the ISM in star-forming galaxies. Their influence may also dominate the relationship between the different interstellar gas phases. How do superbubbles form and evolve? How do they affect the local and global ISM? The Magellanic Clouds provide a superior opportunity to study this shell-forming activity, since both stellar content and gaseous structure can be examined in detail. Here, the results of recent studies of superbubbles in the Magellanic Clouds are reviewed.

Three different topics regarding the ISM in the Magellanic Clouds are discussed. First, we examine how the Magellanic Stream can be used as a tracer of the ionizing radiation leaking out of Galaxy and the Magellanic Clouds. We show that the radiation reaching the Magellanic Stream is less than 1% of the ionizing radiation produced by Galactic 0 and B stars. Since about 14% of the ionizing radiation from these stars is required to ionize the Reynolds layer, which is within 1 kpc of the disk, most of this radiation must be absorbed before reaching the Stream.

Second, we examine the reliability of using CO as a tracer of H2 in regions of low or modest column densities (not giant molecular cloud complexes). For our Galaxy, the usual CO to H2 conversion factor overlooks a considerable amount of H2 and the evidence suggests that this may be true in the LMC as well. Finally, we present numerical hydrodynamical calculations of the interstellar medium in disk galaxies for a region of size 2 kpc along the plane and 15 kpc out of the plane. The simulations reveal a rich structure of low density hot regions separated by cold dense material, with the resulting position velocity diagrams being qualitatively similar to the recent HI studies of the LMC. A number of other aspects of these simulations are discussed also.

A new Hα survey of the Magellanic Clouds which is being carried out on fine-grained Tech-Pan emulsion with the UK 1.2m Schmidt Telescope will have the best combination of depth and resolution of any that cover such a wide area in and around the Magellanic Clouds. Preliminary results show that the films will provide identifications of new emission-line stars and nebulae.

We present results on the SMC from the first full season of the Michigan/CTIO Magellanic Cloud Emission-Line Survey, being carried out from CTIO. Images are being obtained in Hα, [S II] λλ 6717, 6731, and [O III] λ 5007, plus red and green continuum bands for star subtraction. Data from the 1996–97 season have been assembled into large mosaic images which reveal the rich variety of nebulosity in the SMC in unprecedented detail. These are providing definitive samples of the active, occasionally violent, ISM on scales including superbubbles, wind-blown bubbles, supernova remnants, H II regions, and planetary nebulae.