On the determination of dipoles from incomplete galaxy catalogues

The spherical harmonic and random filling methods, used to account for incomplete sky coverage in dipole calculations, are investigated. A study of their comparative performances is carried out and the former method is shown to be more accurate. Using both these methods, an attempt is made to find the regions responsible for the dipole in the Lahav optical catalogue. We find that the Virgo-Centaurus region provides most of the dipole power. We also find strong indications that these structures are embedded within a global underlying anisotropy. (author)