The velocity field of UGC 6697 revisited

Abstract

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 H_alpha frame. Long-slit spectroscopy shows a 500 km s^-1 rigid-body rotation curve with a sudden central velocity jump, of more than 200 km s^-1 amplitude. Fabry-Perot observations of the H_alpha emission line enable us to trace a detailed 2D velocity field, confirming the complex kinematical behaviour, particularly in the circumnuclear 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 be reconciled with the complex velocity field assuming the presence of a second galaxy hidden behind the main body of UGC 6697. Based on observations taken at the ESO/VLT, INT, OHP, CFHT and Loiano telescopes. The INT is operated by the I.N.G. at the Spanish Observatorio del Roque de Los Muchachos of the I.A.C. The OHP is operated by the French CNRS. The Loiano telescope belongs to the University of Bologna (Italy).