2008MNRAS.386..963S

NGC6908, an S0 galaxy situated in the direction of NGC6907, was only recently recognized as a distinct galaxy, instead of only a part of NGC6907. We present 21-cm radio synthesis observations obtained with the Giant Metrewave Radio Telescope (GMRT) and optical images and spectroscopy obtained with the Gemini-North telescope of this pair of interacting galaxies. From the radio observations, we obtained the velocity field and the HI column density map of the whole region containing the NGC6907/8 pair, and by means of the Gemini multi-object spectroscopy we obtained high-quality photometric images and 5 Å resolution spectra sampling the two galaxies. By comparing the rotation curve of NGC6907 obtained from the two opposite sides around the main kinematic axis, we were able to distinguish the normal rotational velocity field from the velocity components produced by the interaction between the two galaxies. Taking into account the rotational velocity of NGC6907 and the velocity derived from the absorption lines for NGC6908, we verified that the relative velocity between these systems is lower than 60 km/s. The emission lines observed in the direction of NGC6908, not typical of S0 galaxies, have the same velocity expected for the NGC6907 rotation curve. Some emission lines are superimposed on a broader absorption profile, which suggests that they were not formed in NGC6908. Finally, the HI profile exhibits details of the interaction, showing three components: one for NGC6908, another for the excited gas in the NGC6907 disc and a last one for the gas with higher relative velocities left behind NGC6908 by dynamical friction, used to estimate the time when the interaction started in (3.4±0.6)x10⁷ yr ago.