NEW DETECTIONS OF LY ALPHA EMISSION IN YOUNG GALAXIES

We report IUE observations of two extremely low-metallicity H II galaxies. Ly alpha emission was detected in both galaxies. Our results confirm previous findings that young br unevolved galaxies exhibit weak or absent Ly alpha emission combined with a strong UV continuum, and that the Ly alpha/H beta ratio and metal content are correlated in the sense that the lower the abundance, the larger the ratio. This supports the hypothesis that in the higher metallicity systems Ly a is destroyed by dust absorption. At redshifts of between 2 and 3, Ly alpha emission comparable to the strongest detected in H II galaxies [L(Ly alpha) approximately 5 x 10(42) erg s-1] would be barely visible; this fact can explain the relative lack of success in detecting Ly alpha emission associated with low-metallicity damped Ly alpha systems in QSOs. Our results cast doubt on claims of detection of high-redshift young galaxies associated with active galaxies, or with strong Ly alpha and both C IV and He II, since they may represent very extended narrow-line regions photoionized by radiation with a power-law spectrum rather than by normal hot stars.