What information about protogalactic gas clouds is contained in quasar absorption lines?
What will be an ideal response?
Quasar absorption lines show the presence of massive clouds of neutral hydrogen between us and the quasar. The hydrogen absorption line is generally wider for higher redshifts, indicating that the most distant clouds are more massive than the older, closer clouds, which have, presumably, converted some of their gas to stars. The absorption lines of heavier elements are stronger, however, at lower redshift, suggesting that the older, closer galaxies have enriched their interstellar medium more than the more distant, younger objects.
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