Ages and Metallicities of Cluster Galaxies in A779 using Modified   Str\"omgren Photometry
  In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using the modified Str\"omgren photometry. But with the considerable debate toward the project's abilities, we re-introduce the system after a thorough testing of repeatability of colors and reproducibility of the ages and metallicities for six common galaxies in the three A779 data sets. A fair agreement has been found between the modified Str\"omgren and Str\"omgren filter systems to produce similar colors (with the precision of 0.09 mag in (uz-vz), 0.02 mag in (bz-yz), and 0.03 mag in (vz-vz)), ages and metallicities (with the uncertainty of 0.36 Gyr and 0.04 dex from the PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but still unable to completely break. We further extend this paper to re-study the evolution of galaxies in the low mass, dynamically poor A779 cluster by correlating the luminosity (mass), density, radial distance with the estimated age, metallicity, and the star formation history. Our results distinctly show the bimodality of the young, low-mass, metal-poor population with the mean age of 6.7 Gyr (\pm 0.5 Gyr) and the old, high-mass, metal-rich galaxies with the mean age of 9 Gyr (\pm 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red, and the downsizing phenomenon. Our analysis shows that the modified Str\"omgren photometry is very well suited for studying low- and intermediate-z clusters, as it is capable of observing deeper with better spatial resolution at spectroscopic redshift limits, and the narrowband filters estimate the age and metallicity with lesser uncertainties compared to other methods that study stellar population scenarios. 
Yuvraj Harsha Sreedhar, Andrew P. Odell, Karl D. Rakos, Gerhard   Hensler, Werner W. Zeilinger
astro-ph.GA