  We address the origin of the golden mass and time for galaxy formation and
the onset of rapid black-hole growth. The preferred dark-halo mass of
~$10^{12}M_\odot$ is translated to a characteristic epoch, z~2, at which the
typical forming halos have a comparable mass. We put together a coherent
picture based on existing and new simple analytic modeling and cosmological
simulations. We describe how the golden mass arises from two physical
mechanisms that suppress gas supply and star formation below and above the
golden mass, supernova feedback and virial shock heating of the circum-galactic
medium (CGM), respectively. Cosmological simulations reveal that these
mechanisms are responsible for a similar favored mass for the dramatic events
of gaseous compaction into compact star-forming "blue nuggets", caused by
mergers, counter-rotating streams or other mechanisms. This triggers inside-out
quenching of star formation, to be maintained by the hot CGM, leading to
today's passive early-type galaxies. The blue-nugget phase is responsible for
transitions in the galaxy structural, kinematic and compositional properties,
e.g., from dark-matter to baryon central dominance and from prolate to oblate
shape. The growth of the central black hole is suppressed by supernova feedback
below the critical mass, and is free to grow once the halo is massive enough to
lock the supernova ejecta by its deep potential well and the hot CGM. A
compaction near the golden mass makes the black hole sink to the galactic
center and triggers a rapid black-hole growth. This ignites feedback by the
Active Galactic Nucleus that helps keeping the CGM hot and maintaining
long-term quenching.
