SEDfit: Software for Spectral Energy Distribution Fitting of Photometric Data

This paper describes SEDfit, the earliest --- but continually upgraded --- software package for spectral energy distribution fitting (SED fitting) of high-redshift photometric data, and the only one to properly treat non-detections. The principles of maximum-likelihood SED fitting are described, including formulae used for fitting both detected and un-detected (upper limits) photometric data. The internal mechanics of the SEDfit package are presented and several illustrative examples of its use are given. The paper concludes with a discussion of several issues and caveats applicable to SED-fitting in general.