Low-mass protogalaxies and absorption lines in quasi-stellar objects

The possibility is explored that the many weak unMentified absorption lines in high-redohift QSO spectra are L lines of hydrogen. The likely existence of a metagalactic flux of ionizing radiation indicates that hydrogen clouds at high redshifts must be thoroughly ionized. Observations of PRL 957 show that the suggested clouds may be low-mass (Al < 1000.7 Al0) protogalaxies. A simple model for the clouds' collapse and for the flux of ionizing radiation is used to compute the distributio of expected Lot lines in the spectrum of a QSO as a function of wavelength and H i column density. The computed distribution is in accord wfth observations of the two most distant QSOs, PRL 957 and 4C 05.34. Crudities in the theory and stronger tests of its validity are also discussed.