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 forma- tion 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 A-7400 A. We clas- sify 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 A 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 MB; lower luminosity systems tend to have larger equivalent widths. 2) The equivalent width ratio (Nii)6583/H is anti-correlated with equivalent width H ;a relationship is given that can be used to remove the (Nii) contribution from blended H+(Nii)6548, 6583. 3) The (Oii), H, H and H 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.