A Virtual Observatory Census to Address Dwarfs Origins. AVOCADO - I.
  Science goals, sample selection and analysis tools
  (Abridged) AVOCADO aims at establishing firm conclusions on the formation and
evolution of dwarf galaxies by constructing and analysing a homogeneous,
multiwavelength dataset for a statistically significant sample of approximately
6500 nearby dwarfs (M_i > -18 mag). We present the sample selection criteria
and describe the suite of analysis tools, some of them developed in the
framework of the Virtual Observatory. We make use of optical spectra and
UV-to-NIR imaging of the dwarf sample to derive SFRs, stellar masses, ages and
metallicities - which are further supplemented with structural parameters that
are used to classify them morphologically. This dataset, coupled with a
detailed characterisation of each dwarf's environment, allows for a fully
comprehensive investigation of their origins and to track the potential
evolutionary paths between the different dwarf types. We characterise the local
environment of all dwarfs in our sample, paying special attention to trends
with current star formation activity. We find that virtually all quiescent
dwarfs are located in the vicinity (projected distances < 1.5 Mpc) of L*
companions, consistent with recent results. While star-forming dwarfs are
preferentially found at separations of the order of 1 Mpc, there appears to be
a tail towards low separations (<100 kpc) in the distribution of projected
distances. We speculate that, modulo projection effects, this probably
represents a genuine population of late-type dwarfs caught upon first infall
about their host and before environmental quenching has fully operated. In this
context, these results suggest that internal mechanisms -such as gas exhaustion
via star formation or feedback effects- are not sufficient to completely cease
the star formation activity in dwarf galaxies, and that becoming the satellite
of a massive central galaxy appears to be a necessary condition to create a
quiescent dwarf.
