Supergalactic studies. IV. Systematic orientation of galaxy clouds relative to the supergalactic plane

The major nearby clouds of galaxies tend to be elongated in directions roughly parallel to the supergalactic plane. Out of 11 clouds (or 12 including the Local Cloud, Paper I) with major axes a>10degree and sufficiently elongated (b/a<0.8) to give an unambiguous direction of elongation, none is inclined to the supergalactic equator by more than 35degree. If the space orientations of the cloud axes were random and uncorrelated, the probability of this happening by chance is 3x10-5 (or 1x10-5 if the Local Cloud is included). In lower supergalactic latitudes (vertical-barBvertical-bar<10degree), the average inclination of six clouds is =20degree with =0.49; in higher latitudes (10degree=23degree with =0.62. Several possible mechanisms leading to this systematic orientation in a flat supercluster are noted. This effect adds greatly to the difficulty of explaining the ''supercluster effect'' as a random clumping accident. The combined probability that the observed distribution of objects discussed in Papers I to IV could arise by chance in the random clumping hypothesis is of the order of 10-12