# 4.1.30. Reds: redshift modelΒΆ

This multiplicative model applies a redshift to an arbitrary additive component. If a photon is emitted at energy , the redshift model will put it at energy . In addition, a time dilatation correction is applied such that the spectrum (expressed as photons/s per bin) is divided by .

However, it is necessary to distinguish two different cases:

Case 1 (flag=0): In this case, the time dilatation correction described above is applied to the spectrum, which makes this the (default) option to be used for cosmological redshifts.

Case 2 (flag=1): By setting this flag, the time dilatation correction to the flux is not applied. This is used for a redshift caused by motion away from us. It should be used for any velocity fields other than the Hubble flow.

Warning

Note that this component should be used in tandem with the distance command (Distance: set the source distance) to take into account the cosmological redshift and its influence on the flux completely.

The parameters of the model are:

`z`

: Redshift . Default value: 0. Dimensionless. Redshifts are
positive, blueshifts negative.`flag`

: Flag: 0 (cosmological redshift) or 1 (velocity redshift).
Default value: 0.