4 Discussion

As is evident already from a visual comparison of the SO and CS maps displayed in Figs. 1-9 rather large variations of SO/CS integrated intensity ratio are apparent within and between the sources. Moreover, as can be seen in Fig. 15, the intensity ratio $I[{\rm SO}]/I[{\rm CS}]$ can in general be used as a tool to find positions where SO/CS abundance variations are likely to occur. In fact, using the results in Fig. 15 we can estimate that the SO/CS abundance ratio varies between 0.25-4.5. This crude estimate indeed reflects large abundance variations as will be advocated, based upon a more thorough analysis, in Paper II.

In a subsequent Paper III (Olofsson et al., in prep.) we plan to derive the true abundance variations with respect to H₂ in all the sources catalogued in this paper. The H₂ column density mapping information is currently being accumulated in terms of C¹⁸O(1-0) mapping.

Acknowledgements

We thank the referee, L. Pagani, for constructive comments on the manuscript. The authors wish to thank the Swedish National Space Board (Rymdstyrelsen) for substantial Odin astronomy funding. PB and ÅH also acknowledge partial support by the Swedish National Science Research Council (NFR).