Searching for Intermediate Mass Black Holes in galaxies with Low
  Luminosity AGN: A multiple-method approach
  Aims: This work is the first stage of a campaign to search for IMBHs, in low
luminosity AGN (LLAGN) and dwarf galaxies. An additional, and equally
important, aim of this pilot study is to investigate the consistency between
the predictions of several BH scaling relations and the fundamental plane of
black hole activity (FP-BH). Methods: We use X-ray and radio luminosity
relations in accreting BHs, along with the latest scaling relations between the
mass of the central black hole (MBH) and the properties of its host spheroid,
to predict MBH in seven LLAGN, that were previously reported to be in the IMBH
regime. Namely, we use the recently re-evaluated MBH - Msph (Msph : spheroid
absolute magnitude at 3.6 microm) scaling relation for spiral galaxies, the MBH
- nsph (nsph : major axis Sersic index of the bulge) relation, the MBH - PA
(PA: pitch angle) relation and the FP-BH for weakly accreting BHs, to
independently estimate MBH in all seven galaxies. Results: We find that all
LLAGN in our list have low-mass central black holes - with log MBH/Msol~6.5 on
average - but they are, not IMBHs. All 4 methods used predicted consistent BH
masses, in the 1sigma range. Furthermore, we report that, in contrast to
previous classification, galaxy NGC 4470 is bulge-less, and cast doubts on the
AGN classification of NGC 3507. Conclusions: We find that our latest,
state-of-the-art techniques for bulge magnitude & Sersic index computations and
the most recent updates of the MBH - Lsph, MBH - nsph , MBH - PA relations and
the FP-BH produce consistent results in the low mass regime. We establish a
multiple method approach for predicting BH masses in the regime where their
spheres-of- grav. influence cannot be spatially resolved. Our approach
mitigates against outliers from any one relation and provides a more robust
average prediction. We will use our new method to revisit more IMBH candidates
in LLAGN
