astropy: Problems with redshifted Gaussian example in compound model docs
One of the model composition examples (see https://astropy.readthedocs.org/en/latest/modeling/compound-models.html#model-composition) implements a RedshiftedGaussian
model. However, there are two issues. First, the Gaussian appears to be blueshifted instead of redshifted, assuming the currently unlabeled (it should be labeled) x-axis is wavelength (see https://astropy.readthedocs.org/en/latest/modeling/compound-models-1.png). The green z=0
Gaussian appears to be at the largest wavelength (and the line is broadest).
The second issue is more subtle, but important. Redshifting a spectrum/emission line, etc. involves more than just transforming the wavelengths. There needs to be a corresponding transformation to conserve flux, e.g. wave’ = wave * (1 + z) and flux’ = flux / (1 + z). Again looking at the “redshifted” Gaussian figure, notice that the integrated line flux is changing with redshift because the line width is changing. There needs to be a corresponding amplitude change to conserve integrated flux.
About this issue
- Original URL
- State: closed
- Created 9 years ago
- Comments: 28 (28 by maintainers)
It was never meant to be a “physical” example–just a demonstration of composing models. But if this makes it more palatable I’m all for it 😃
Okay, how about this?