Relative Orientation of Pairs of Spiral Galaxies in the Sloan Digital Sky Survey

Abstract

We find, from our study of binary spiral galaxies in the Sloan Digital Sky Survey Data Release 6, that the relative orientation of disks in binary spiral galaxies is consistent with their being drawn from a random distribution of orientations. For 747 isolated pairs of luminous disk galaxies, the distribution of phi, the angle between the major axes of the galaxy images, is consistent with a uniform distribution on the interval [0 degrees, 90 degrees]. With the assumption that the disk galaxies are oblate spheroids, we can compute cos(beta), where beta is the angle between the rotation axes of the disks. In the case that one galaxy in the binary is face-on or edge-on, the tilt ambiguity is resolved, and cos(beta) can be computed unambiguously. For 94 isolated pairs with at least one face-on member, and for 171 isolated pairs with at least one edge-on member, the distribution of cos(beta) is statistically consistent with the distribution of cos(i) for isolated disk galaxies. This result is consistent with random orientations of the disks within pairs.