Results & Discussion

The results from our initial observations mapped on a 2 arcmin grid show the CO emission to extend over 3 degrees in the northwest-southeast direction. This is in agreement with the Carina GMC identified in the Columbia survey (Grabelsky et al. 1981). Our higher resolution map reveals a very clumpy morphology with two strong emission areas; one centred on Car II and the other towards a region northwest of the optical emission. Here we present the results from the better sampled set of observations on a 1 arcmin grid towards the Car II region.

A grey-scale and contour image of the 12CO(1-0) emission integrated over a velocity range of -35 to 0 km/s is shown in Fig 1. The grey-scale boundaries show the region that was observed. Clearly two main emission regions are identified; a large region of emission covering the north-western part of the map and a region of fainter emission located in the south-east corner. These are the northern and southern emission clouds first distinguished by de Graauw et al. (1981) from observations of 12CO(2-1) emission using a beamwidth of 2.2 arcmin and sampled on a 4 arcmin grid.

  
Figure 1: The grey-scale and contour image of the 12CO(1-0) emission integrated over a velocity range of -30 to 0 km/s. The contour levels are 16, 22, 28, 34, 40, 46, 52, 58, 64, 67, 70, 82, 88, 94, 100 percent of the peak intensity, 2.0 10 K ms Beam. The faint grey emission shows the total observing area.

The northern cloud contains the strongest emission. 12CO(1-0) observations of this region were first made by Whiteoak & Otrupcek (1984) using a 2.8 arcmin beam revealing three emission concentrations. The higher resolution data presented here clearly show a more complicated morphology. Most of the strong emission is located in a large central region with branches of fainter emission extending outwards from it. One emission branch extends westwards and then expands outwards past the observed region. This emission is part of the larger GMC which extends over 2 degrees to the northwest. The strongest integrated emission is located in a small concentration at the southern part of the central emission region. Here the integrated intensity reaches a maximum of 2.0 x 10 K ms beam. The southern cloud is a region of fainter emission, breaking up into small clumps at its southern edge.

The northern and southern cloud are separated by a region where the integrated CO emission is below 10 percent of the peak integrated intensity. This region is centred on the keyhole and Car II region. We did detect CO emission from the small-scale clumps that were found by Cox & Bronfman (1995); however the integrated intensity map shown in Fig 1 is not sensitive to such small-scale distributions.

Our results have identified many small CO concentrations in both the northern and southern cloud. These could be dense, warm clumps where star formation may next occur. In fact, Megeath et al. (1996) have detected very faint reddened stars towards one of the CO clumps in the southern cloud. If these are very recently formed stars as suggested then this is the first evidence of ongoing star formation within the Carina nebula. We are currently carrying out further observation towards the many clumps defined by this initial set of observations to look for further evidence of ongoing star formation.

  
Figure 2: Typical spectra of the 12CO(1-0) emission at nine positions throughout the northern and southern cloud. Positions are given in B1950 coordinates.

Some sample spectra taken towards nine positions throughout the nebula are shown in Fig 2. The first three spectra (a-c) are representative of the southern cloud region. The emission is largely at a velocity of -27 km/s with a second component at -20 km/s seen at the western edge of the cloud. The remaining six spectra (d-i) are taken at positions in the northern cloud. Most of the emission in this northern region is found between velocities of -27 to -8 km/s. The southern and eastern part of the cloud (d,e) has emission largely at -27, -18 and -10 km/s whereas for the northern and western region the main emission components are at -20 and -10 km/s. The velocities presented here agree with those obtained by de Graauw et al. (1981).

Figure 3 shows an expanded view of the area centred on the Keyhole Nebula. The contours represent the peak integrated 12CO(1-0) emission distribution and are superimposed on R-band image showing the H distribution, obtained from the Digitised Sky Survey (DSS). The figure provides a comparison between the locations of Tr 14, Tr 16 and the optical nebulosity with the distribution of molecular gas. The keyhole region and the associated Car II radio continuum source appear to have little interaction with the main cloud emission. This supports the idea of the surrounding GMC being dispersed by the stellar winds and ionising fluxes of the massive stars in this region (Cox & Bronfman 1995). The southern cloud emission is confined to the eastern dust lane and coincides with an optical depth maximum. In the north the CO emission extends over the optical emission but the peak emission is located to the west of Tr 14 towards the western dust lane. It is coincident with a far-infrared emission peak. Adjacent to the eastern side of the CO emission peak is the radio continuum peak Car I. The sequence of the distinct emission sources; ionising cluster - radio continuum peak - far-IR-peak has been explained using a strong gradient in gas and dust density increasing from Tr 14 to the dust lane to the west (Harvey et al. 1979). de Graauw et al. (1981) described this region as a blister-type region, whereby the edge of the molecular cloud is being externally ionised by Tr 14. Our observations, which show a strong CO concentration adjacent to the radio continuum source Car I, support this blister-type model and clearly define the interface of the ionised and molecular gas.

  
Figure 3: A contour representation of the 12CO(1-0) emission integrated over a velocity range of -30 to 0 km/s, superimposed on a R-band image. The contour levels are 10, 16, 22, 28, 34, 40, 46, 52, 58, 64, 67, 70, 82, 88, 94, 100 percent of the peak intensity, 2.0 x 10 K ms Beam. Tr 14 is concentrated in the northwest corner of the map and Tr 16 is situated near the centre.

© Copyright Astronomical Society of Australia 1997