Lyman α emission from galaxies: the case of absorption line selected galaxies at z~0.3-0.4.

Abstract

Three galaxies, at moderate redshifts (z~0.3-0.4) and identified as causing MgII absorption lines in the spectra of the quasars 0229+131, 1127-145 and 1209+107, have been observed with the Faint Object Spectrograph on-board the Hubble Space Telescope. The spectra have been obtained with the large aperture (4.3x1.4" effective), at a resolution (point-source) of R=~1300 and in the wavelength range (observed frame) 1570-2320A. A possible, weak Lyα emission is reported for G0229+131. A faint continuum may be present in all three spectra at the longest wavelengths. Both the Lyα detection and the Lyα upper limits derived for the other two objects, are lower than predicted from their respective Hβ or [OII] intensities. This result indicates a significant extinction at Lyα. In the case of G1209+107, enhanced extinction accompanying the Lyα resonant multiple scattering is responsible for the Lyα depletion. The results are consistent with both the weakness (or the lack) of Lyα emission from normal galaxies at high redshift, and the trend of Lyα depletion as a function of metallicity observed in nearby star-forming galaxies.