A Virtual Observatory Census to Address Dwarfs Origins. AVOCADO - I. Science goals, sample selection and analysis tools

Abstract

(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.

13 pages, 12 figures (a few with degraded resolution). Final version accepted to A&A

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