Starbursts and black hole masses in X-shaped radio galaxies: Signatures
  of a merger event?
  We present new spectroscopic identifications of 12 X-shaped radio galaxies
and use the spectral data to derive starburst histories and masses of the
nuclear supermassive black holes in these galaxies. The observations were done
with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San
Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of
X-shaped radio galaxies studied with optical spectroscopy. We show that the
combined sample of the X-shaped radio galaxies has statistically higher
black-hole masses and older episodes of star formation than a control sample of
canonical double-lobed radio sources with similar redshifts and luminosities.
The data reveal enhanced star-formation activity in the X-shaped sample on the
timescales expected in galactic mergers. We discuss the results obtained in the
framework of the merger scenario.
