On the three-dimensional structure of edge-on disc galaxies

A simple algorithm is employed to deproject the two-dimensional images of a pilot sample of 12 high-quality images of edge-on disc galaxies and to study their intrinsic three-dimensional (3D) stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dust lane. This could be explained by the widespread presence of a thick disc component in these galaxies. In addition, the 3D view allows the study of the vertical distribution of the outer disc, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated discs. This could be regarded as a weakening of the 'truncation' with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.