We are grateful to G. De Francesco for her collaboration during observations and data reduction. We wish to thank F. Scaltriti and G. Massone for useful discussions. This research has made use of the STScI Digitized Sky Survey (DSS) and of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank the referee (Dr. P. Véron) for his prompt report and useful comments.
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