Gravitational Redshift of Emission Lines in the AGN Spectra
  The detection of gravitationally redshifted optical emission lines has been
reported just for a few active galaxies. In this paper we give a short overview
of studies that analyzed or exploited the detection of the gravitational
redshift in optical AGN spectra. In addition, we tested the consistency of
gravitational redshift as the physical origin of the redward shifts observed in
their spectra using a sample of $\approx$ 50 Hamburg-ESO intermediate to high
redshift quasars that are among the most luminous quasars known ($10^{47}
\lesssim L \lesssim 10^{48}$ erg/s), and are expected to host very massive
black holes. To this aim we modeled the line profile with accretion disk models
around a black hole.
