This research has made use of the NASA/IPAC extragalactic database (NED), which is operated by the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration. A.C. Gonçalves acknowledges support from the Junta Nacional de Investigação Científica e Tecnológica, Portugal, during the course of this work (PhD. grant PRAXIS XXI/BD/5117/95).
© European Southern Observatory (ESO) 1998
Online publication: April 28, 1998