Spectroscopic study of blue compact galaxies. II. Spectral analysis and correlations

This is the second paper in a series studying the star formation rates, stellar components, metallicities, and star formation histories and evolution of a sample of blue compact galaxies. We analyzed spectral properties of 97 blue compact galaxies, obtained with the Beijing Astronomical Observatory (China) 2.16 m telescope, with spectral range 3580 Å-7400 Å. We classify the spectra according to their emission lines: 13 of the total 97 BCG sample are non-emission line galaxies (non-ELGs); 10 have AGN-like emission (AGNs), and 74 of them are star-forming galaxies (SFGs). Emission line fluxes and equivalent widths, continuum fluxes, the 4000 Å Balmer break index and equivalent widths of absorption lines are measured from the spectra. We investigate the emission line trends in the integrated spectra of the star-forming galaxies in our sample, and find that: 1) The equivalent widths of emission lines are correlated with the galaxy absolute blue magnitude M_B; lower luminosity systems tend to have larger equivalent widths. 2) The equivalent width ratio [N II]6583/Hα is anti-correlated with equivalent width Hα; a relationship is given that can be used to remove the [N II] contribution from blended Hα+ [N II]6548, 6583. 3) The [O II], Hβ , Hγ and Hα fluxes are correlated; those can be used as star formation tracers in the blue. 4) The metallicity indices show trends with galaxy absolute magnitude and attenuation by dust, faint, low-mass BCGs have lower metallicity and color excess. Tables 1-4, and 6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/396/503