Discussion

Thus far 21-cm surveys have been bedevilled by short integrations. To complete half the sky in a couple of years will force integration times per pointing below 1000 secs, with the danger of missing the most interesting sources, such as intergalactic hydrogen clouds. The way round this is to have 3 surveys going on concurrently: A shallow all-sky survey with secs; a Very Deep Patch with (Section 4) and an Intermediate Deep Patch of around 100 pointings, each around secs, aimed say in Sculptor where there is already known to be a lot of HI. Hopefully, we then won't miss very much.

Finally, it is worth reminding ourselves that the Universe is dominated by Dark Matter. Were it otherwise, then the Iceberg galaxies which we hope to find, would probably all have been torn apart. But dim galaxies are not necessarily light galaxies. Malin 1 has a 350 km wide rotation curve (). The exciting work of de Blok et al. (1996), who have measured the rotation curves of a number of moderately dim galaxies show that their mass-to-light ratios rise systematically as their SBs fall. Combining this with the recent discovery (Bergeron 1997) that dim and dwarf galaxies may be the absorbers responsible for QSOALs, it may yet turn out that dim galaxies contain most of the galaxy mass (and light) in the cosmos. The multibeam surveys at Parkes and Jodrell Bank will probably find out.

© Copyright Astronomical Society of Australia 1997