The Peculiar Optical Spectrum of 4C+22.25: Imprint of a Massive Black Hole Binary?
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We report the discovery of peculiar features in the optical spectrum of
4C+22.25, a flat spectrum radio quasar at z = 0.4183 observed in the
Sloan Digital Sky Survey and in a dedicated spectroscopic follow-up from
the Nordic Optical Telescope. The Hβ and Hα lines show broad
profiles (FWHM ~ 12,000 km s<SUP>-1</SUP>), faint fluxes, and extreme
offsets (Δv = 8700 ± 1300 km s<SUP>-1</SUP>) with respect
to the narrow emission lines. These features show no significant
variation in a time lag of ~3.1 yr (rest frame). We rule out possible
interpretations based on the superposition of two sources or on
recoiling black holes, and discuss the virtues and limitations of a
massive black hole binary scenario.