In article <1150714093.532568.131280@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"sean" <jaymoseley@xxxxxxxxxxx> writes:
> This is the quote from gcn 5237..."A preliminary analysis
> shows the Lya forest up to a rather weak Lya line, "
> Isnt that the same as a weak L break?
Nope. The Lyman alpha line is at rest 122 nm; the "break" is at rest
91 nm. The "forest" is between these wavelengths, corresponding to
gas along the line of sight but less redshifted than the background
> For instance Im still unsure of what exactly the `Lyman limit` is.
It's another word for the break. Physically, the Lyman alpha
absorption line is a transition from the n=1 to n=2 level of
hydrogen. The "break" is a transition from n=1 to the electron being
separated from the nucleus. Only photons near 122 nm in the rest
frame can easily be absorbed and make a line, but _any_ photon with
wavelength <91 nm can be absorbed. The absorption cross section
decreases, though, as the wavelength gets shorter.
Steve Willner Phone 617-495-7123 swillner@xxxxxxxxxxxxxxx
Cambridge, MA 02138 USA
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