Authors: Filippos Koliopanos, Bogdan C. Ciambur, Alister W. Graham, Natalie A. Webb, Mickael Coriat, Burçin Mutlu-Pakdil, Benjamin L. Davis, Olivier Godet, Didier Barret, and Marc S. Seigar.
Aims. This work is the first stage of a campaign to search for
intermediate mass black holes (IMBHs), in low luminosity AGN (LLAGN)
in dwarf galaxies. An additional, and equally important, aim of this
pilot study is to investigate the consistency between the predictions
of several popular BH scaling relations and the fundamental plane (FP)
of BH activity (FP-BH).
Methods. We use well established X-ray and radio luminosity relations
in accreting black holes, 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 μm) scaling
relation for spiral galaxies, the MBH–nsph
(nsph: major axis Sérsic index of the spheroid
component) relation, the MBH–PA (PA:
spiral-arm pitch angle) relation and a recently re-calibrated version
of 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/MSun) = 6.5 on
average — but they are, most likely, not IMBHs. All four methods
used estimate consistent BH masses, in the 1σ range.
Furthermore, we report that, in contrast to previous classification,
galaxy NGC 4470 is bulge-less, and we also cast doubts on the AGN
classification of NGC 3507.
Conclusions. We find that, our latest, state-of-the-art techniques for
bulge magnitude and Sérsic 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 therefore establish a multiple method approach for
predicting BH masses in the regime where their
spheres-of-(gravitational 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