Introduction

The Carina HII region/molecular cloud complex is an excellent region for studying the interaction of massive stars with their parental Giant Molecular Cloud (GMC). The nebula covers an area of 4 deg and is bisected by a prominent V-shaped dark lane. There are over 14 star clusters in this region which have been studied extensively over the past twenty years. For excellent reviews see Feinstein (1995) and Walborn (1995). The most influential clusters of the nebula are the two OB clusters, Tr 14 and Tr 16. These clusters contain numerous O-type stars, including three O3 stars each, making them two of the most massive star clusters in our galaxy. Tr 14 is a compact cluster situated to the north-west of the nebula, adjacent to the western dust lane. Tr 16 is an open cluster centred northwards of the vertex of the dark lane. It contains one of the most massive stars known: Car. Here we will adopt the popular view (e.g. Tovmassian 1995, Walborn 1995) that Tr 14 and Tr 16 are at a common distance of about 2.2 kpc and that Tr 14 is younger than Tr 16.

Considering the extensive studies on the stellar content of the Carina Nebula, in particular Car and its surrounding Homunculus nebula, relatively little work has been done on the extended nebula in the last fifteen years. Early radio continuum observations revealed that the nebula contains a large ionised region with two peaks, Car I and Car II (Gardner & Morimoto 1968). Higher resolution radio continuum data show that both Car I and Car II are made up of a number of filamentary arcs and rings and are everywhere thermal (Retallack 1983, Whiteoak 1994). Car II is located to the north of Car and Car I is located towards the western dark lane, just west of Tr 14. The dynamics of the ionised gas in this region have been studied via hydrogen recombination line emission (Gardner et al. 1970, Huchtmeier & Day 1975) and H and [NII] emission observations (Deharveng & Maucherat 1975). The results show line splitting towards the Car II region which has been interpreted as an expanding shell of ionised gas.

The dark lanes consist of molecular gas and dust that are associated with the nebula (Dickel 1974). HCO and OH absorption measurements identified two optical depth maxima which were located towards these lanes (Gardner, Dickel & Whiteoak 1970, Dickel & Wall 1974). Extended far-IR emission is confined there also (Harvey Hoffmann & Campbell 1979, Ghosh et al. 1988). There are two main CO emission regions towards the nebula; a northern and southern cloud (de Graauw et al. 1981, Whiteoak & Otrupcek 1984). Both regions are part of a much larger GMC which has a projected length of 130 pc and a mass in excess of 510 Msun (Grabelsky et al. 1988). The area between the southern and northern CO clouds is centred on the Keyhole Nebula, a dense dark cloud northwest of Car. Here the molecular gas exists in dense clumps of typical mass 10 Msun that are separated both in space and velocity (Cox & Bronfman 1995).

The picture used to describe the Carina complex is one in which the massive star clusters, Tr 14 and Tr 16, are interacting strongly with the molecular cloud from which they formed. It is generally accepted that the photons from Tr 14 and Tr 16 are responsible for the ionised emission of Car I and Car II respectively, and that their strong stellar winds are producing the general expansion of the nebula.

We are undertaking a multi-wavelength study of the Carina Complex in order to study the detailed kinematics and distribution of the molecular and ionised gas and to look for further evidence of ongoing star formation. Here we present the results of initial observations of the 12CO(1-0) emission. CO emission is thermalised in both low- and high-density gas and therefore is suitable for tracing the overall distribution and velocity structure of the molecular cloud. It also can pinpoint any `CO hot-spots'. These are warm molecular cores where stars could possibly be forming.

© Copyright Astronomical Society of Australia 1997