4 Conclusions

From complete mapping of the molecular gas in the near-by sample of Curran et al. (2000) and comparing the results with those for the distant sample, it appears that:

1.

We had not previously mapped most of the CO in the near-by galaxies.

2.

This is also true for the HCN which is much less confined that previously thought.

3.

There does exist a distinct difference between the near-by and distant sample.

Elaborating on this last point, it seems that there is a selection effect in which we only detect the very FIR luminous galaxies ( ) at recessional velocities in excess of $\approx$4000 km s^-1. These galaxies have either incredibly high HCN/CO luminosity ratios ($\approx$1 as in Mrk 273, Curran et al. 2000) within their star forming regions or, unlike the near-by galaxies, the CO is extremely confined resulting in little contamination by this molecule in the galactic disk.
As well as this we find:

1.

Low global CO $2\rightarrow 1/1\rightarrow 0$ ratios for two thirds of the sample, possibly suggesting sub-thermally excited CO;

2.

No significant differences in the CO luminosities between the type 1 and type 2 Seyferts of the sample;

3.

That the HCN/CO ratio in the near-by sample increases with proximity to the nucleus, possibly further increasing in beyond the region of powerful star formation.

Although this latter point and our other analysis may hint at an increased AGN (cf. stellar) contribution to the FIR emission in the near-by and distant galaxies (respectively), we feel that the key to this puzzle is not improved statistics but actual mapping of the molecular gas distributions in these sources. Such projects would require interferometric observations which should prove to be worthwhile projects, particularly for the more distant galaxies, when very high resolution interferometers (such as ALMA) become available.

Acknowledgements

We wish to thank the referee R. Antonucci for his prompt and helpful comments as well as Kate Brooks at the La Silla 3.6 m telescope for her advice. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.