In recent years, increasing attention has been devoted to semi-empirical, data-driven models to tackle some aspects
of the complex and still largely debated topic of galaxy formation and evolution. We here present a new semiempirical
model whose marking feature is simplicity: it relies on solely two assumptions, one initial condition and
two free parameters. Galaxies are connected to evolving dark matter haloes through abundance matching between
specific halo accretion rate (sHAR) and specific star formation rate (sSFR). Quenching is treated separately, in a
fully empirical way, to marginalize over quiescent galaxies and test our assumption on the sSFR evolution without
contaminations from passive objects. Our flexible and transparent model is able to reproduce the observed stellar
mass functions up to z ∼ 5, giving support to our hypothesis of a monotonic relation between sHAR and sSFR. We
then exploit the model to test a hypothesis on morphological evolution of galaxies. We attempt to explain the
bulge/disk bimodality in terms of the two halo accretion modes: fast and slow accretion. Specifically, we speculate
that bulge/spheroidal components might form during the early phase of fast halo growth, while disks form during
the later phase of slow accretion. We find excellent agreement with both the observational bulge and elliptical mass
functions.
