Orientations of very faint galaxies in the Coma cluster

Abstract

We have then searched for preferential orientations of faint galaxies in the Coma cluster (down I_Vega~-11.5). By applying a deconvolution method to deep u* and I band images of the Coma cluster, we were able to recover orientations down to faint magnitudes. No preferential orientations are found in more than 95% of the cluster, and the brighter the galaxies, the fewer preferential orientations. The minor axes of late type galaxies are radially oriented along a northeast -southwest direction and are oriented north-south in the western X-ray sub- structures. For early type galaxies, in the western regions showing significant preferential orientations, galaxy major axes are oriented perpendicularly to the north-south direction. In the eastern significant region and close to NGC 4889, galaxy major axes also point toward the 2 cluster dominant galaxies. In the southern significant regions, galaxy planes are tangential with respect to the clustercentric direction, except close to (alpha=194.8, delta=27.65) where the orientation is close to -15deg. Part of the orientations of the minor axes of late type galaxies and of the major axes of early type galaxies can be explained by a tidal torque model applied to cosmological filaments and local merging directions. Another part (close to NGC4889) can be accounted for by collimated infalls. For early type galaxies, the (alpha=194.8, delta=27.65) region shows orientations that probably result from processes involving induced star formation.