Stellar Mass and Velocity Functions of Galaxies: Backward evolution and
  the fate of Milky Way siblings
  We attempt in this paper to check the consistency of the observed Stellar
Mass Function (SMF), SFR functions and the cosmic star formation rate density
with simple backward evolutionary models. Starting from observed SMF for
star-forming galaxies, we use backwards models to predict the evolution of a
number of quantities, such as the SFR function, the cosmic SFR density and the
Velocity Function. The velocity being a parameter attached to a galaxy during
its history (contrary to the stellar mass), this approach allows us to quantify
the number density evolution of galaxies of a given velocity, e.g. of the Milky
Way siblings. Observations suggest that the SMF of star forming galaxies is
constant between redshift 0 and 1. In order to reproduce this result, we must
quench star formation in a number of star forming galaxies. The SMF of these
quenched galaxies is consistent with available data concerning the increase in
the population of quiescent galaxies in the same redshift interval. The SMF of
quiescent galaxies is then mainly determined by the distribution of active
galaxies that must stop star formation, with a modest mass redistribution
during mergers. The cosmic SFR density, and the evolution of the SFR functions
are relatively well recovered, although they provide some clue for a small
evolution of the SMF of star forming galaxies at the lowest redshifts. We thus
consider that we have obtained in a simple way a relatively consistent picture
of the evolution of galaxies at intermediate redshifts. We note that if this
picture is correct, 50 percent of the Milky-Way sisters (galaxies with the same
velocity as our Galaxy, i.e. 220 km/s) have quenched their star formation since
redshift 1 (and an even larger fraction for larger velocities). We discuss the
processes that might be responsible for this transformation.
