Estimating black hole masses in obscured AGN using X-rays
  Determining the black hole masses in active galactic nuclei (AGN) is of
crucial importance to constrain the basic characteristics of their central
engines and shed light on their growth and co-evolution with their host
galaxies. While the black hole mass (MBH) can be robustly measured with
dynamical methods in bright type 1 AGN, where the variable primary emission and
the broad line region (BLR) are directly observed, a direct measurement is
considerably more challenging if not impossible for the vast majority of
heavily obscured type 2 AGN. In this work, we tested the validity of an
X-ray-based scaling method to constrain the MBH in heavily absorbed AGN. To
this end, we utilized a sample of type 2 AGN with good-quality hard X-ray data
obtained by the nuSTAR satellite and with MBH dynamically constrained from
megamaser measurements. Our results indicate that, when the X-ray broadband
spectra are fitted with physically motivated self-consistent models that
properly account for absorption, scattering, and emission line contributions
from the putative torus and constrain the primary X-ray emission, then the
X-ray scaling method yields MBH values that are consistent with those
determined from megamaser measurements within their respective uncertainties.
With this method we can therefore systematically determine the MBH in any type
2 AGN, provided that they possess good-quality X-ray data and accrete at a
moderate to high rate.
