Stromgren Photometry from z = 0 to z ≈ 1. I. The Method

We use rest-frame Stromgren photometry to observe clusters of galaxies in aself-consistent manner from z=0 to z=0.8. Stromgren photometry of galaxies isan efficient compromise between standard broad-band photometry andspectroscopy, in the sense that it is more sensitive to subtle variations inspectral energy distributions than the former, yet much less time-consumingthan the latter. Principal Component Analysis (PCA) is used to extract maximuminformation from the Stromgren data. By calibrating the Principal Componentsusing well-studied galaxies (and stellar population models), we develop apurely empirical method to detect, and subsequently classify, cluster galaxiesat all redshifts smaller than 0.8. Interlopers are discarded with unprecedentedefficiency (up to 100%). The first Principal Component essentially reproducesthe Hubble Sequence, and can thus be used to determine the global starformation history of cluster members. The (PC2, PC3) plane allows us toidentify Seyfert galaxies (and distinguish them from starbursts) based onphotometric colors alone. In the case of E/S0 galaxies with known redshift, weare able to resolve the age-dust- metallicity degeneracy, albeit at theaccuracy limit of our present observations. This technique will allow us toprobe galaxy clusters well beyond their cores and to fainter magnitudes thanspectroscopy can achieve. We are able to directly compare these data over theentire redshift range without a priori assumptions because our observations donot require k-corrections. The compilation of such data for different clustertypes over a wide redshift range is likely to set important constraints on theevolution of galaxies and on the clustering process.Comment: 35 pages, 18 figures, accepted by ApJ