LYMAN-ALPHA ABSORPTION IN INTERGALACTIC HYDROGEN
On the cosmological hypothesis one expects continuous absorption at wavelengths
below the Lyman-alpha emission (Scheuer, Gunn and Peterson).
We illustrate it taking 3C 9 as an example. 3C 9 has a redshift of 2.012 so
that the strong Lyman-alpha line of hydrogen, which is normally observed at
1216 Å, is shifted to 3663 Å. The intergalactic neutral hydrogen
density is estimated, by indirect methods, to be about 10^-29 g/cm^-3. The
passage of continuum radiation through this hydrogen will give an absorption
line at 1216 Å. In the case of distant objects like 3C 9 sufficient
hydrogen should be traversed to give a detectable effect. Since radiation
from this distant quasar is red-shifted, the absorption will be evident not
as a line but as a general deficiency of continuum radiation at wavelengths
between 1216 and 3663 Å. The absorption takes place at 1216 Å but the
photons absorbed would arrive at the earth at a wavelength shifted by an
amount appropriate to the distance between the point of absorption and the
earth. Observational measurements have shown no absorption. Our theory
resolves this problem quite easily. Galactic stars are not expected to show
any such absorption and neither are quasars.
Next Section: Proper Motions of Quasars