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The equation of state of the intergalactic medium
Joop Schaye (IoA)
The thermal evolution of the intergalactic medium (IGM) depends on the
reionization history of the universe. Numerical simulations indicate
that the low density IGM, which is responsible for the low column
density Lyman-alpha forest, follows a well defined temperature-density
relation. We demonstrate that this results in a cutoff in the
distribution of line widths (b-parameters) as a function of column
density (N). This explains the existence of the lower envelope which
is clearly seen in scatter plots of the b(N)-distribution in observed
QSO spectra. We use simulations to determine the relation between the
cutoff and the effective equation of state and apply this relation to
Keck spectra. In this way we are able to probe the thermal history of
the IGM from z=4 to 2.
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