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 3580Å – 7400Å. We classify the spectra according to their emission lines: 13 of the total 97 BCGs 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 MB ; lower luminosity systems tend to have larger equivalent widths. 2) The equivalent width ratio [N ii]6583/Hα is anticorrelated 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. Subject headings: galaxies: active – galaxies: compact – galaxies: general – galaxies: stellar content