We acknowledge the referee, A. Omont, for the useful suggestions. We thank Raphael Moreno and Goeran Sandell who did some of the observations in service mode at the IRAM and JCMT telescopes respectively, and Roberto Fanti for useful discussions. This work was supported in part by the Formation and Evolution of Galaxies network set up by the European Commission under contract ERB FMRX-CT96-086 of its TMR programme and by the high-z programme subsidy granted by the Netherlands Organization for Scientific Research (NWO). RJI is supported by a PPARC Advanced Fellowship.
© European Southern Observatory (ESO) 1998
Online publication: December 8, 1997