The velocity field of UGC 6697 revisited

The edge-on galaxy UGC 6697 has a peculiar morphological appearance: a high surface brightness SE component and what appears to be a tidal tail with blue color and low surface brightness extending toward the NW, as dramatically evidenced in subarcsecond broad band images taken with the VLT and in a deep Ha frame. Long-slit spectroscopy shows a 500 km/s rigid-body rotation curve with a sudden central velocity jump, of more than 200 km/s amplitude. Fabry-Perot observations of the Ha emission line enable us to trace a detailed 2D velocity field, confirming the complex kinematical behaviour, particularly in the circuninuclear region where multiple velocity components are clearly superposed on the same line of sight. This region hosts a double nucleus and shows sudden color and metallicity gradients, which can he reconciled with the complex velocity field assuming the presence of a second galaxy hidden behind the main body of UGC 6697.