Galaxy downsizing evidenced by hybrid evolutionary tracks
  An unified picture of stellar and halo mass build-up as a function of mass is
presented. Inferred stellar-dark halo mass relations of galaxies, Ms-Mh, out to
z=4 together with average LCDM halo mass aggregation histories (MAHs) are used
for inferring average Ms growth histories, the Galaxian Hybrid Evolutionary
Tracks (GHETs). The more massive the galaxy, the earlier transited in average
from an active regime of Ms growth to a passive one:
log(Mtran/Msun)=10.30+0.55z ("population downsizing"), where Mtran is the
typical transition stellar mass. This result agrees with independent
observational determinations based on the evolution of the galaxy stellar mass
function decomposition into blue and red galaxies. The specific star formation
rate, SSFR, predicted from the derivative of the GHET is consistent with direct
measures of the SSFR for galaxies at different z's. The average GHETs of
galaxies smaller than Mtran at z=0 (Ms~10^10.3 Msun) did not reach the
quiescent regime, and for them, the lower the mass, the faster the later Ms
growth rate ("downsizing in SSFR"). The GHETs allow to predict the transition
rate in number density of active to passive population; the predicted values
agree with direct estimates of growth rate in number density for the (massive)
red population up to z~1. We show that LCDM-based models of disk galaxy
evolution are able to reproduce the low-mass side of the Ms-Mh relation at z~0,
but at higher z's disagree strongly with the GHETs: models do not reproduce the
downsizing in SSFR and the high SSFR of low mass galaxies. (Abridged)
