Quenching and Galaxy Demographics
  The open-data revolution in astronomy is forcing the community to develop
sophisticated analysis methods that heavily rely on realistic simulations. The
phenomenology of the evolution of galaxy demographics can be described by a set
of continuity equations invoking two quenching mechanisms: mass quenching and
satellite quenching. The combination of these two mechanisms produces a double
Schechter function for the quiescent population, as is observed in the
low-redshift universe. In this paper we consider these quenching mechanisms,
explicitly including satellite galaxies, and add the exact time evolution of
the star-forming population. These new features complete the current versions
of these continuity equations, and are essential for the realistic simulations
required in modern extra-galactic astrophysics. We derive the analytical
relation between the quiescent and the active populations, reducing
considerably the parameter space for the simulation. In addition, we derive the
analytical time dependence of the amplitude of the Schechter function. Finally,
we validate our results against the SDSS DR7 galaxy sample. The model will be
implemented in the SkyPy library and the main plots sonified using STRAUSS.
