ULTRAVIOLET TO NEAR-INFRARED SPECTRAL DISTRIBUTIONS OF STAR-FORMING GALAXIES - METALLICITY AND AGE EFFECTS

Spectral distributions from the UV to the near-IR of a sample of 44 st ar-forming galaxies are used to calculate the metallicity (O/H), star- formation rate (SFR) and age of the starbursts. The oxygen abundance c overs the range 8.3 < O/H < 9.4, and nitrogen (N) is found to be mostl y a product of secondary nucleosynthesis for O/H > 8.4. Due to its sec ondary origin, N/O ratios up to almost-equal-to 4 times the solar valu e can be obtained for metal-rich starbursts. The SFR ranges from 0.01 to 100 M. yr-1. The lower metallicity galaxies seem to be experiencing an instantaneous burst of star formation, with ages ranging from unde r 5 x 10(6) to 10(7) yr. The highest metallicity galaxies are most pro bably experiencing a continuous burst. Correlations between the calcul ated quantities and several spectral features are investigated. We fou nd a highly significant correlation between the equivalent width W(C i v lambda1550)-a stellar (absorption) feature-and the oxygen abundance of the emitting gas (O/H). Thus we show for the first time that the st ellar metallicity is well correlated with the gas metallicity in star- bursting galaxies. The equivalent width W(Si IV lambda1400) and the em ission line ratio [N II] lambdalambda6548,84/Halpha also correlate wel l with O/H, and all three features can be used as metallicity indicato rs for star-forming galaxies. The continuum color between lambda1400 a nd lambda3500 [C(14-35)] is shown to correlate with O/H, although it i s better correlated with E(B- V). It was not possible to disentangle t he metallicity from the reddening effect in C(14-35). We estimate that the reddening affecting the UV continuum is about half the one derive d from the Balmer decrement of the emitting gas. The SFR correlates we ll with the galaxy luminosity and there is no dependence of the contin uum color on the SFR. The higher metallicities are only found in the m ore luminous galaxies, while low metallicities are found over the whol e luminosity interval (-16 < M(B) < - 23, H-0 = 50 km s-1 Mpc-1) cover ed by the sample.