UV/Optical attenuation by the intergalactic medium.
This model is now in the Xspec release and this page is superceded by the Xspec manual
This multiplicative model computes the mean attenuation of the
optical/UV spectrum of an object at redshift z at a random position on
the sky due to intergalactic medium (IGM) clouds following either
Madau (1995, ApJ 441, 18) or Meiksin (2006, MNRAS, 365, 807).
The model calculates the mean expected attenuation due to resonant
scattering by Lyman transitions and photoelectric absorption shortward
of the Lyman limit. Attenuation by Helium and metals are not included
in the Meiksin model, but are expected to be small. The total
attenuation is set to zero for wavelengths less than 900 Angstroms.
The user chooses whether to include attenuation due to photoelectric
absorption.
par1 = z: redshift
par2 = model: Use Madau (0) or Meiksin (1 or greater)
par3 = photoelectric absorption included (1) or not (0)
To install this model download the source code
(zigm.f) and the model parameter description file
(zigm.dat).
