6 Conclusions

We have presented an optical/near-infrared imaging and HI database for a complete sample of 15 HI-selected dwarf galaxies in the Hydra I cluster. The absolute blue magnitude of their optical counterparts ranges between -15.1 mag and -17.5 mag and their HI mass to blue luminosity between 0.1 and $2.4 M_{\odot}/L_{\odot,B}$. Their integrated B-I color index varies between 0.8 and 1.7 mag. The low surface brightness components of half of the Hydra dwarfs have an undisturbed exponential profile; the remaining galaxies either show a flattening of their SBP in the central regions or a truncation in the outer regions. One of the HI sources lying in the vicinity of a HI-rich spiral has no optical counterpart.

The heterogeneity of the sample may well be due to the variety of the local environment of each galaxy: in particular the pressure of the intra-cluster medium and the density of the galaxy population. Indeed the dwarfs in Hydra are not uniformly distributed and tend to cluster in substructures, like the more massive galaxies (Valluri et al. 1999). The presence of companions, as commonly observed for the HI-rich dwarfs, may directly affect their morphology and their star formation history. In this paper, we have remarked on these issues on a case-by-case basis only. We will present a general discussion on the role of the environment on the global properties of the Hydra HI-rich dwarfs in another article of these series.

Acknowledgements

This work has greatly benefited from discussions with J. van Gorkom. We are grateful to the 2p2 team at la Silla who helped us with the observations, especially Isabel Peres and Thomas Augusteijn for their efficient and friendly introductions at the D1.5 m and 2.2 m telescopes. We wish to thank our referee, C. Carignan, for valuable comments. Research by P.P. has been supported by Deutsche Agentur für Raumfahrtangelegenheiten (DARA) GmbH grant 50 OR 9407 6. The Unité Scientifique Nançay of the Observatoire de Paris is associated as USR B704 to the French Centre National de Recherche Scientifique (CNRS). Nançay also gratefully acknowledges the financial support of the Région Centre in France. DAEC, the Department of Extragalactic Astronomy and Cosmology of the Observatoire de Paris is associated with the Université de Paris 7 and as URA 173 to the CNRS. This research has made use of the Lyon-Meudon Extragalactic Database (LEDA) supplied by the LEDA team at the CRAL-Observatoire de Lyon (France), as well as of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.