Spectroscopy of Dwarf HII Galaxies in the Virgo Cluster. I. Data, Chemical Abundances and Ionization Structure

Long-slit spectroscopy has been obtained for a sample of 22 blue dwarf galaxies selected in the direction of the Virgo Cluster as part of a larger sample of Virgo blue dwarf galaxies for which deep Halpha imaging has been collected. Most of the galaxies in the present sample appear classified as BCDs or dwarf Irregulars in the Virgo Cluster Catalog. Line fluxes, Hbeta equivalent width and extinction coefficients, spatial emission profiles, ionization structure and physical conditions are presented for the galaxies of the sample. Chemical abundances have been derived either using a direct determination of the electron temperature or after detailed examination of the predictions of different empirical calibrations. The oxygen abundance derived for the sample of Virgo dwarf galaxies span in the range 7.6 < 12 + log O/H < 8.9, and the corresponding nitrogen to oxygen abundance ratio cover from values typical of low metallicity field BCD galaxies up to near solar.