Origine delle radio-galassie a X: proprieta' morfologiche e spettrofotometriche

X-shaped radio galaxies are a peculiar subclass of radio galaxies, they show a pair of secondary extended radio lobes, or wings, in addiction to the primary ones. In order to investigate the formation mechanism of these sources we compare the radio emission to the properties of the host galaxy, we perform a spectral analysis, which allows us to determine the stellar population age, and we study the emission lines properties. In the past years, two mechanisms are hypotized to be responsible for this peculiar morphology sources: a realignment of the jet of the black hole or a hydrodinamical mechanism. The orientation of the wings shows a strong connection with the host galaxy orientation as they are preferentially aligned with its minor axis. The spectral analysis reveals that these galaxies are characterized by an old stellar population. The study of the emission lines properties does not reveal any peculiar feature compared to normal radio-galaxies. On the basis of these results we support the hydrodinamical mechanism as responsible of the formation of X-shaped radio galaxies and we exclude a jet realignment, since it would not predict a correlation between the position angles and it would bring to a high star formation rate.