An off-centered active galactic nucleus in NGC 3115
  NGC 3115 is an S0 galaxy that has always been considered to have a pure
absorption-line spectrum. Some recent studies have detected a compact
radio-emitting nucleus in this object, coinciding with the photometric center
and with a candidate for the X-ray nucleus. This is evidence of the existence
of a low-luminosity active galactic nucleus (AGN) in the galaxy, although no
emission line has ever been observed. We report the detection of an
emission-line spectrum of a type 1 AGN in NGC 3115, with an H$\alpha$
luminosity of $L_{H\alpha} = (4.2 \pm 0.4) \times 10^{37}$ erg s$^{-1}$. Our
analysis revealed that this AGN is located at a projected distance of $\sim
0.29" \pm 0.05"$ (corresponding to $\sim 14.3 \pm 2.5$ pc) from the stellar
bulge center, which is coincident with the kinematic center of this object's
stellar velocity map. The black hole corresponding to the observed off-centered
AGN may form a binary system with a black hole located at the stellar bulge
center. However, it is also possible that the displaced black hole is the
merged remnant of the binary system coalescence, after the "kick" caused by the
asymmetric emission of gravitational waves. We propose that certain features in
the stellar velocity dispersion map are the result of perturbations caused by
the off-centered AGN.
