Reconstructing Galaxy Spectral Energy Distributions from Broadband Photometry

We present a novel approach to photometric redshifts, one that merges theadvantages of both the template fitting and empirical fitting algorithms,without any of their disadvantages. This technique derives a set of templates,describing the spectral energy distributions of galaxies, from a catalog withboth multicolor photometry and spectroscopic redshifts. The algorithm isessentially using the shapes of the templates as the fitting parameters. Fromsimulated multicolor data we show that for a small training set of galaxies wecan reconstruct robustly the underlying spectral energy distributions even inthe presence of substantial errors in the photometric observations. We applythese techniques to the multicolor and spectroscopic observations of the HubbleDeep Field building a set of template spectra that reproduced the observedgalaxy colors to better than 10%. Finally we demonstrate that these improvedspectral energy distributions lead to a photometric-redshift relation for theHubble Deep Field that is more accurate than standard template-basedapproaches.Comment: 23 pages, 8 figures, LaTeX AASTeX, accepted for publication in A