  We study the dynamics of the scalar field FLRW flat cosmological models
within the framework of the Unified Dark Matter (UDM) scenario. In this model
we find that the main cosmological functions such as the scale factor of the
Universe, the scalar field, the Hubble flow and the equation of state parameter
are defined in terms of hyperbolic functions. These analytical solutions can
accommodate an accelerated expansion, equivalent to either the dark energy or
the standard $\Lambda$ models. Performing a joint likelihood analysis of the
recent supernovae type Ia data and the Baryonic Acoustic Oscillations traced by
the SDSS galaxies, we place tight constraints on the main cosmological
parameters of the UDM cosmological scenario. Finally, we compare the UDM
scenario with various dark energy models namely $\Lambda$ cosmology, parametric
dark energy model and variable Chaplygin gas. We find that the UDM scalar field
model provides a large and small scale dynamics which are in fair agreement
with the predictions by the above dark energy models although there are some
differences especially at high redshifts.
