Orientations of very faint galaxies in the Coma cluster

TL;DR

This study investigates the orientations of very faint galaxies in the Coma cluster, revealing patterns related to galaxy type and location, and suggesting influences from tidal torques, infalls, and star formation processes.

Contribution

The paper provides the first detailed analysis of faint galaxy orientations in the Coma cluster down to very low magnitudes, using a novel deconvolution method to recover orientations.

Findings

No significant preferential orientations in over 95% of the cluster.

Late type galaxies' minor axes are radially oriented in certain regions.

Early type galaxies show orientations consistent with tidal torque and infall models.

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.