Eight dwarf starburst galaxies have been observed with the Caltech Submillimeter Observatory (CSO) telescope in the CO J= 3 -2 transition. The galaxies observed are He 2-10, NGC 5253, NGC 1569, NGC 3077, Haro 2, Haro 3, II Zw 40 and Mrk 86; all but the last two are detected. The central regions of He 2-10 and NGC 5253 were mapped and a CO(2-1) spectrum of NGC 5253 was obtained. The error weighted mean CO(3-2)/CO(1-0) ratio of the detected galaxies is 0.60±0.06, which is virtually identical to what is found for starbursts in the nuclei of nearby spirals, and suggests that the molecular gas is optically thick, warm (T k > 20 K), and moderately dense (n H2 ∼ 10 3−4 cm −3 ). The CO(3-2)/CO(1-0) ratio peaks at or close to the starburst in all cases. CO emission does not appear to be optically thin in these dwarfs, despite the low metallicity and intense radiation fields, which is probably because in order for CO to exist in detectable amounts it must be self-shielding and hence optically thick. Physical properties of the molecular clouds in these dwarf starbursts appear to be essentially the same as nearby spiral nuclei, with the possible exception that CO is more confined to the cloud cores.

We report subarcsecond-resolution VLA and Keck mid-infrared imaging of the dwarf starburst galaxy II Zw 40. II Zw 40 contains a bright, compact thermal radio and infrared source with all the the characteristics of a collection of dense HII regions ionized by at least 14,000 O stars. The supernebula is revealed to be multiple sources within an envelope of weaker emission. The radio emission is dominated by free-free emission at 2 cm, and the spectrum of this emission appears to be rising. This suggests that the free-free emission is optically thick at 2 cm, and that the individual HII regions are ∼1 pc in size. This complex of "supernebulae" dominates the total infrared luminosity of II Zw 40, although the radio source is less than ∼150 pc in diameter. Multiple super star clusters appear to be forming here, the much larger analogues of large Galactic HII region complexes.

Little is known about the origins of globular clusters, which contain hundreds of thousands of stars in a volume only a few light years across. Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy NGC5253. The lines arise in gas heated by a cluster of about one million stars, including 4,000-6,000 massive, hot 'O' stars. It is so young that it is still enshrouded in gas and dust, hidden from optical view. The gases within the cluster seem bound by gravity, which may explain why the windy and luminous O stars have not yet blown away those gases. Young clusters in 'starbursting' galaxies in the local and distant Universe may also be gravitationally confined and cloaked from view.

We present 38Aresolution Very Large Array 21 cm continuum and H I line emission observations of the spiral galaxy IC 342, at an adopted distance of 2 Mpc. Kinematic evidence exists for a m \ 2 spiral density wave in the inner disk with a corotation radius located at 4 kpc and a possible four-arm pattern in the outer disk. On smaller scales, outside of the central depression in H I column density, H I is organized into a complex pattern of relatively short (D2È5 kpc), interconnected, spiral arm segments. Numerous "" holes ÏÏ are distributed throughout the H I disk. By considering the e †ects of shear, structures that are not self-gravitating, such as holes and voids, cannot be long-term phenomena. The timescale, combined with the total energy required to evacuate holes, leads us to reject wind and supernovae origins for the large-scale pattern of H I holes in IC 342. Gravitational instabilities in the disk form on a timescale that is short compared with the rotation period of the disk. The pattern of H I spiral arm segments exists on a scale that is consistent with their being material arms that result from gravitational instabilities. The H I cavities are a natural remnant of the process.

We report subarcsecond-resolution VLA imaging of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, compact radio continuum sources are identified in the central ∼ 15 ′′ × 15 ′′ region. These compact sources are responsible for 20 -30 % of the total emission from the central kpc of the host galaxies at 2 cm, but only ∼ 5 -10 % at 6 cm. More than half of the compact sources appear to be H ii regions. The H ii regions with rising spectra must be fairly dense (n i ∼ 10 4 cm −3 ) and are presumably very young.The largest of these H ii regions require the excitation of 500 -800 O stars, within regions of only few parsecs extent. These clusters approach the sizes expected for globular clusters. Thermal free-free emission from compact sources contributes more significantly at 2 cm, while diffuse synchrotron emission dominates at 6 cm. The radio H ii regions are found near the centers of giant molecular clouds in projection, and do not have obvious visual counterparts.