MEASURING BLACK HOLE MASSES IN ACTIVE GALACTIC NUCLEI USING THE POLARIZATION OF BROAD EMISSION LINES

Supermassive black holes (SMBHs) reside in the heart of nearly every mas-
sive galaxy in the Universe. Most of them lie dormant, but when the nearby gas is
abundant, it will enter an active phase and form an active galactic nucleus (AGN). In
their active phase, SMBHs have a profound effect on the host galaxy evolution and its
environment. Reliable SMBH mass measuring is therefore an important task in modern
astronomy. For that purpose, a method has been recently proposed by Afanasiev &
Popović (2015) that uses the rotation of the polarization plane position angle across
the broad emission line profile in order to trace the Keplerian motion and determine
the SMBH mass. This method assumes that broad lines are emitted from a flattened
disk-like region undergoing Keplerian motion, while the polarization is mainly due to
the light scattering of the inner side of the coplanar dusty torus – the equatorial scat-
tering. The goal of the thesis is to theoretically explore the possibilities of this method.
We performed numerous Monte Carlo simulations for modeling equatorial scattering
in AGNs using the radiative transfer code stokes (Goosmann & Gaskell 2007). We
included complex motion of the emitting region in the form of radial inflows, vertical
outflows, or due to the presence of the supermassive binary black holes (SMBBHs). We
also selected four well known AGNs for observations: NGC 4051, NGC 4151, 3C 273 and
PG0844+349. Spectropolarimetry was done with the 6 m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Science (SAO RAS) with the
focal reducer SCORPIO. We modeled each of these AGNs using observational data
available from the literature, and we compared the results of our models with obser-
vational data. We find that this method can be used as a new independent way to
measure the SMBH masses in AGNs. The influence of the inflows and the outflows
can be ignored if they are much lower than the Keplerian velocity. Additionally, when
the scattering region is close to the broad line region, this method becomes indepen-
dent of the viewing inclination. For SMBBHs, this method cannot be used, however,
we obtained unique polarization profiles which are not common for a single SMBH,
which could be used for identifying possible SMBBH candidates. SMBH mass esti-
mates for the four observed AGNs are in good agreement with the masses obtained
using other methods, such as the method of reverberation mapping. Method for inde-
pendent SMBH mass measurements has been theoretically and experimentally verified
in this work, which is very important for the future research that is dealing with the
SMBH influence on its immediate environment.