synphot.reddening.etau_madau(wave, z, **kwargs)[source]

Madau 1995 extinction for a galaxy at given redshift. This is the Lyman-alpha prescription from the photo-z code BPZ.

The Lyman-alpha forest approximately has an effective “throughput” which is a function of redshift and rest-frame wavelength. One would multiply the SEDs by this factor before passing it through an instrument filter.

This approximation is from Footnote 3 of Madau et al. (1995). This is claimed accurate to 5%. The scatter in this factor (due to different lines of sight) is huge, as shown in Madau’s Fig. 3 (top panel); The figure’s bottom panel shows a redshifted version of the “exact” prescription.

Parameters
wavearray-like or Quantity

Redshifted wavelength values. Non-redshifted wavelength is wave / (1 + z).

znumber

Redshift.

kwargsdict

Equivalencies for unit conversion, see validate_quantity().

Returns
extcurveExtinctionCurve

Extinction curve to apply to the redshifted spectrum.