The off-centered Seyfert-like compact emission in the nuclear region of
  NGC 3621
  We analyze an optical data cube of the nuclear region of NGC 3621, taken with
the integral field unit of the Gemini Multi-object Spectrograph. We found that
the previously detected central line emission in this galaxy actually comes
from a blob, located at a projected distance of 2.14" +/- 0.08" (70.1 +/- 2.6
pc) from the stellar nucleus. Only diffuse emission was detected in the rest of
the field of view, with a deficit of emission at the position of the stellar
nucleus. Diagnostic diagram analysis reveals that the off-centered emitting
blob has a Seyfert 2 spectrum. We propose that the line-emitting blob may be a
"fossil" emission-line region or a light "echo" from an active galactic nucleus
(AGN), which was significantly brighter in the past. Our estimates indicate
that the bolometric luminosity of the AGN must have decreased by a factor of
~13 - 500 during the last ~230 years. A second scenario to explain the
morphology of the line-emitting areas in the nuclear region of NGC 3621
involves no decrease of the AGN bolometric luminosity and establishes that the
AGN is highly obscured toward the observer but not toward the line-emitting
blob. The third scenario proposed here assumes that the off-centered
line-emitting blob is a recoiling supermassive black hole, after the
coalescence of two black holes. Finally, an additional hypothesis is that the
central X-ray source is not an AGN, but an X-ray binary. This idea is
consistent with all the scenarios we proposed.
