mboquien
commented
1 year ago Hello. The best fit does not necessarily correspond to the peak. The PDF represents the total likelihood of all the models at a given redshift. However there can be different models at a given redshift, not all of them given a good fit. Conversely the highest likelihood model can be at a different redshift, with many models at that redshift not fitting well.
In your specific case the SED has a powerlaw-like shape. This makes it particularly difficult to constrain the redshift at it lacks defining features (e.g. the Balmer break). This is a usual problem with AGN host galaxies.
Hello!
I am having an issue when estimating redshift values using CIGALE. I get a mismatch between the 'best redshift' in the results.txt/SED plot and the highest peak redshift in the probability distribution function (PDF).
I am interested in obtaining a photometric redshift for certain sources, but I am first testing the program using sources for which I have trustworthy spectroscopic redshifts. I have yet to obtain a match between the spectroscopic redshift and the estimated redshift using CIGALE. However, when I check the PDF for 'universal.redshift', the highest peak is at the correct redshift. Is there a reason for this mismatch? Is there something I can do to improve it? Is it simply a bad SED fit? Or is there another parameter that is affecting the 'best redshift' result. See below:
PDF for redshift: 0_universe.redshift_pdf.pdf SED fitting for same source (with 'best redshift'): 0_best_model.pdf
The actual redshift is z = 1.49004. The highest peak is near 1.5, but the PDF is also very wide, with multiple smaller peaks.
Thank you in advance!