  From high-resolution images of 23 Seyfert-1 galaxies at z=0.36 and z=0.57
obtained with the Near Infrared Camera and Multi-Object Spectrometer on board
the Hubble Space Telescope (HST), we determine host-galaxy morphology, nuclear
luminosity, total host-galaxy luminosity and spheroid luminosity. Keck
spectroscopy is used to estimate black hole mass (M_BH). We study the cosmic
evolution of the M_BH-spheroid luminosity (L_sph) relation. In combination with
our previous work, totaling 40 Seyfert-1 galaxies, the covered range in BH mass
is substantially increased, allowing us to determine for the first time
intrinsic scatter and correct evolutionary trends for selection effects. We
re-analyze archival HST images of 19 local reverberation-mapped active galaxies
to match the procedure adopted at intermediate redshift. Correcting spheroid
luminosity for passive luminosity evolution and taking into account selection
effects, we determine that at fixed present-day V-band spheroid luminosity,
M_BH/L_sph \propto (1+z)^(2.8+/-1.2). When including a sample of 44 quasars out
to z=4.5 taken from the literature, with luminosity and BH mass corrected to a
self-consistent calibration, we extend the BH mass range to over two orders of
magnitude, resulting in M_BH/L_sph \propto (1+z)^(1.4+/-0.2). The intrinsic
scatter of the relation, assumed constant with redshift, is 0.3+/-0.1 dex (<0.6
dex at 95% CL). The evolutionary trend suggests that BH growth precedes
spheroid assembly. Interestingly, the M_BH-total host-galaxy luminosity
relation is apparently non-evolving. It hints at either a more fundamental
relation or that the spheroid grows by a redistribution of stars. However, the
high-z sample does not follow this relation, indicating that major mergers may
play the dominant role in growing spheroids above z~1.
