SED Fitting

Photometric redshift accuracy depends on the number and distribution of filters, photometric depth, and galaxy type. With 10+ filters and good photometry, photo-z uncertainties can be as low as 0.1(1+z) for well-measured galaxies. However, for faint or high-redshift galaxies, or those with poor filter coverage, uncertainties can be 0.3(1+z) or larger, making catastrophic errors possible.

A young, dusty galaxy can have a similar SED to an older, less dusty galaxy because dust reddening mimics stellar age. Similarly, low-metallicity populations and high-redshift nebular emission can produce similar SED shapes. These degeneracies mean that multiple models can fit the data equally well, leading to uncertain parameter estimates. Using many filters, spectroscopic follow-up, or prior information can break degeneracies.

Different codes use different stellar population synthesis models, may include different physical processes (nebular emission, AGN), employ different fitting algorithms, and make different assumptions about priors. These differences can lead to systematic offsets in estimated quantities like stellar mass. Comparing multiple codes is advisable for important analyses, and consensus values reduce systematic effects.