Estimating Fixed-Frame Galaxy Magnitudes in the Sloan Digital Sky Survey

Broad-band measurements of flux for galaxies at different redshifts measuredifferent regions of the rest-frame galaxy spectrum. Certain astronomicalquestions, such as the evolution of the luminosity function of galaxies,require transforming these magnitudes into redshift-independent quantities. Toprepare to address these astronomical questions, investigated in detail insubsequent papers, we fit spectral energy distributions (SEDs) to broad bandphotometric observations, in the context of the optical observations of theSloan Digital Sky Survey (SDSS). Linear combinations of four spectral templatescan reproduce the five SDSS magnitudes of all galaxies to the precision of thephotometry. Expressed in the appropriate coordinate system, the locus of thecoefficients multiplying the templates is planar, and in fact nearly linear.The resulting reconstructed SEDs can be used to recover fixed frame magnitudesover a range of redshifts. This process yields consistent results, in the sensethat within each sample the intrinsic colors of similar type galaxies arenearly constant with redshift. We compare our results to simpler interpolationmethods and galaxy spectrophotometry from the SDSS. The software that generatesthese results is publicly available and easily adapted to handle a wide rangeof galaxy observations.Comment: 28 pages, 14 figures, submitted to A