lumdist vs zred when fitting rest-frame spectra & photometry

[Mslob]

Hi,

At the moment I'm trying to fit the rest-frame spectra and photometry (separately) of a sample of stacked LEGA-C spectra. I'm running into some issues with the lumdist and zred parameters. At the moment I'm trying to fit using zred = 0 and a lumdist defined according to the redshift of the main galaxy in my stack.

This is giving me issues with the overall scaling of the fitted model-spectra, as well as unfeasibly small best-fits for tage. I think this issue comes from how Prospector deals with cosmological dimming when zred = 0, as it doesn't multiply the spectrum by a factor when only lumdist is given (as far as I understand).

Is there an easy way to deal with this additional factor during the model fitting? Or is it simply not possible to fit my sources (z > 0.6) in rest-frame and should I just fit them in observed frame?

Thanks!

[bd-j]

Hi @Mslob thanks for the question. Indeed fitting in the observed frame might be the easiest. You could also maybe divide the stacked fnu spectrum by (1+zred_main) yourself before fitting it while keeping zred=0. However, I don't think such an overall normalization issue should affect tage (unless you are running up against total mass prior limits). That sounds like another issue, and the solution probably depends on which SFH model you're using.

[bd-j]

Assuming this is resolved, but please reopen if there are further questions or issues!