The supergalactic plane revisited with the Optical Redshift Survey

We re-examine the existence and extent of the planar structure in the local galaxy density field, the so-called supergalactic plane (SGP). This structure is studied here in three dimensions using both the new Optical Redshift Survey (ORS) and the IRAS 1.2-Jy redshift survey. The density contrast in a slab of thickness 20h^-1Mpc and diameter 80Mpc aligned with the standard de Vaucouleurs supergalactic coordinates is δ_sgp~0.5 for both ORS and IRAS. The structure of the SGP is not well described by a homogeneous ellipsoid, although it does appear to be a flattened structure, which we quantify by calculating the moment of inertia tensor of the density field. The directions of the principal axes vary with radius, but the minor axis remains within θ_z~30 deg of the standard SGP Z-axis, out to a radius of 80h^-1Mpc, for both ORS and IRAS. However, the structure changes shape with radius, varying between a flattened pancake and a dumbbell, the latter at a radius of ~50h^-1Mpc, where the Great Attractor and Perseus-Pisces superclusters dominate the distribution. This calls to question the connectivity of the `plane' beyond ~40h^-1Mpc. The configuration found here can be viewed as part of a web of filaments and sheets, rather than as an isolated pancake-like structure. An optimal minimum variance reconstruction of the density field using Wiener filtering, which corrects for both redshift distortion and shot noise, yields a similar misalignment angle and behaviour of axes. The background-independent statistic of axes proposed here can be best used for testing cosmological models by comparison with N-body simulations.