6 Summary

In this paper, we have measured the fluxes and equivalent widths of emission lines, the fluxes at several points of the continuum, the 4000 Å Balmer break index, and the equivalent widths of absorption lines for our BCGs sample. Then we have analyzed the fluxes and equivalent widths of emission lines for the star-forming galaxy subsample.

Our main results are:

1.

We have measured the fluxes and equivalent widths of emission lines for BCGs, and estimated their errors. The typical uncertainties of the measurements are less than 10% for the brightest H$\alpha$6563, H$\beta$4861, [O  II]3727, [O  III]4959,5007, [N  II]6583, [S  II]6717,6731 lines and less than 20% for the weaker H$\gamma$4340, He  I5876, [O  I]6300  and [O  III]4363 lines. Our line intensity ratios are in good agreement with those of previous works.The color excesses due to internal extinction was calculated based on the flux ratio of H$\alpha$/H$\beta$.

2.

The equivalent widths of absorption features, the continuum colors and the 4000 Å Balmer break indices of BCGs were measured. The mean certainty in these measurements is better than 15%.

3.

The equivalent width of H$\alpha$  emission line is correlated with M_B; lower luminosity systems tend to have larger equivalent widths. This can be explained by assuming blue galaxies dominate the faint SFG population, while redder galaxies dominate the bright SFG population.

4.

On average, luminous BCGs are likely to be enhanced in nitrogen abundance. This suggests that in faint, low-mass, BCGs nitrogen is a primary element, whereas in brighter, more massive BCGs nitrogen comes from a secondary source.

5.

A correlation is found between most of emission lines, the strongest correlations are found between [O  II]3727, H$\gamma$, H$\beta$ and H$\alpha$. Besides [O  II]3727, H$\gamma$ and H$\beta$ lines can serve as a reliable star formation tracers for strong emission line galaxies.

6.

Metallicity indices show clear trends with galaxy absolute magnitude, confirming that there is a relation in galaxies between the overall metallicity of the star forming regions and the galaxy luminosity. Faint, low-mass BCGs have lower metallicity and internal extinction.

Acknowledgements

We thank the referee Dr. Y. I. Izotov for his valuable comments, constructive suggestions on the manuscript. This work is based on observations made with the 2.16 m telescope of the Beijing Astronomical Observatory(BAO) and supported by the Chinese National Natural Science Foundation (CNNSF 10073009). S. Charlot thanks the Alexander von Humboldt Foundation, the Federal Ministry of Education and Research, and the Programme for Investment in the Future (ZIP) of the German Government for support. X. Kong has been financed by the Special Funds for Major State Basic Research Projects of China and the Alexander von Humboldt Foundation of Germany.