AGN BLR structure, luminosity and mass from combined Reverberation
  Mapping and Optical Interferometry observations
  Unveiling the structure of the Broad Line Region (BLR) of AGN is critical to
understand the quasar phenomenon. Detail study of the geometry and kinematic of
these objects can answer the basic questions about the central BH mass,
accretion mechanism and rate, growth and evolution history. Observing the
response of the BLR clouds to continuum variations, Reverberation Mapping (RM)
provides size vs luminosity and mass vs luminosity relations for QSOs and Sy1
AGNs with the goal to use these objects as standard candles and mass tags.
However, the RM size can receive different interpretations depending on the
assumed geometry and the corresponding mass depends on an unknown geometrical
factor as well on the possible confusion between local and global velocity
dispersion. From RM alone, the scatter around the mean mass is as large as a
factor 3. Though BLRs are expected to be much smaller than the current spatial
resolution of large optical interferometers (OI), we show that differential
interferometry with AMBER, GRAVITY and successors can measure the size and
constrain the geometry and kinematics on a large sample of QSOs and Sy1 AGNs.
AMBER and GRAVITY (K around 10.5) could be easily extended up to K equal to 13
by an external coherencer or by advanced incoherent data processing. Future
VLTI instrument could reach K around 15. This opens a large AGN BLR program
intended to obtain a very accurate calibration of mass, luminosity and distance
measurements from RM data which will allow using many QSOs as standard candles
and mass tags to study the general evolution of mass accretion in the Universe.
This program is analyzed with our BLR model allowing predicting and
interpreting RM and OI measures together and illustrated with the results of
our observations of 3C273 with the VLTI.
