Abstract. The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100 000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted models. For instance, raw 21-cm line widths are transformed into mean standard widths after correction for instrumental effect and then into maximum velocity rotation properly corrected for inclination and non-circular velocity. This paper presents the reduction formulae for each parameter: coordinates, morphological type and luminosity class, diameter and axis ratio, apparent magnitude (UBV , IR, HI) and colors, maximum velocity rotation and central velocity dispersion, radial velocity, mean surface brightness, distance modulus and absolute magnitude, and group membership. For each of these parameters intermediate quantities are given: galactic extinction, inclination, K-correction etc.. All these parameters are available from direct connexion to LEDA and distributed on a standard CD-ROM (PGC-ROM 1996) by the Observatoire de Lyon via the CNRS.

No abstract

In this paper we present a new redshift survey undertaken to address the rather interesting question that arises when all the currently available redshift information from the LEDA database is plotted in`hypergalactic' coordinates. A signi cant empty region was found between the southern Pavo-Indus (PI) wall and the northern Perseus-Pisces (PP) chain. This survey tests the reality of this void which may simply re ect previous poor sampling of the galaxies in this region. Redshifts for a magnitude selected sample of 379 galaxies were obtained covering the four UKST/SERC survey elds: #537, #470, #346, #290 with 15:5 B T 17:0. All redshifts were obtained with the FLAIR multi-object spectroscopy system on the 1.2 m U.K. Schmidt Telescope at Siding Spring, Australia. Two highly signi cant density enhancements were found in the galaxy distribution at 133Mpc and 200Mpc (H 0 =75 km.s 1 .Mpc 1 ). We claim that no connexion exists between PP and PI. However, a southern extension of PP was detected and makes the total length of this chain of more than 150 Mpc.