At UNSW we have obtained results for the first extragalactic carbon monoxide (CO) survey conducted at Mopra. We successfully observed galaxies as distant as 45 megaparsecs (over 146 million light years). Our survey of 35 southern spiral galaxies yielded 19 detections in CO, with 12 first time detections.

These are important results – the CO content and distribution within a galaxy enables us to estimate the mass of the galaxy, gives details of the density profile and underlying structure of the galaxy, and allows us to estimate star formation rates and associated molecular depletion rates.

Results of this survey and northern CO surveys will also give us valuable information on CO content and distribution within spiral galaxies, and will assist us in developing more accurate star formation models. An immediate application of our survey will be to select targets for follow up surveys of rarer and less bright star formation tracers, which together with information from CO surveys and data on brighter molecules will enable us to assemble profiles of density distributions and turbulence and in particular understand the role of chaos in activating star formation.

Below are CO spectra obtained for two of our new CO detections – NGC1566 located 19.3 megaparsecs from us, and NGC1792 at 16.2 megaparsecs distance. Our results are consistent with data obtained from optical and HI (neutral hydrogen) surveys. Features evident from both spectra are the self absorption of CO emission within the galaxy nucleus, outer CO clouds being contained within the previously observed HI region, and asymmetrical blue and red shifted CO emission peaks arising from the rotation of the spiral arms.

A unique feature of our extragalactic CO survey is that it was instigated in conjunction with a CO survey of a region within our own galaxy – the Delta Quadrant Survey – also conducted at Mopra by UNSW astronomers. As we can eliminate specific observing variables such as observing location and telescope characteristics from the comparison of galactic and extragalactic CO results, we have an unprecedented opportunity to directly compare the features of CO distribution in our own galaxy against nearby spiral galaxies.

Fig. 1: NGC1566 and its CO spectra Fig. 2: NGC1792 and its CO spectra

Patricia Sparks