Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.260....3t&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 260, no. 1, p. 3-8.
Astronomy and Astrophysics
Astronomy
40
Active Galaxies, Emission Spectra, Galactic Evolution, H Ii Regions, Lyman Alpha Radiation, Abundance, Iue, Red Shift, Star Formation Rate, Stellar Radiation, Ultraviolet Spectra
Scientific paper
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 or 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-alpha 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) about 5 x 10 to the 42nd erg/s 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 H II, since they may represent very extended narrow-line regions photoionized by radiation with a power-law spectrum rather than by normal hot stars.
Diaz Angeles I.
Terlevich Elena
Terlevich Roberto
Vargas Maria L. G.
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