Ages and Metallicities of Cluster Galaxies in A779 Using Modified Strömgren Photometry

Abstract

In the quest for the formation and evolution of galaxy clusters, Rakos and coworkers introduced a spectrophotometric method using the modified Strömgren photometry. But with the considerable debate toward the project's abilities, we re-introduce the system by testing for the repeatability of the modified Strömgren colors and compare them with the Strömgren colors, and check for the reproducibility of the ages and metallicities (using the Principle Component Analysis (PCA) technique and the GALEV models) for the six common galaxies in all the three A779 data sets. As a result, a fair agreement between two filter systems was found 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)) and the generated ages and metallicities are also similar (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, (as it was not elaborately analyzed by Rakos and co-workers in their previous work) 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 (± 0.5 Gyr) and the old, high-mass, metal-rich galaxies with the mean age of 9 Gyr (± 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red (Butcher-Oemler phenomenon), and the downsizing phenomenon. Our analysis shows that the modified Strömgren 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

Age and Metallicity of galaxies in different environments of the Coma supercluster

“…There are several ways to break this age-Z degeneracy. While some studies employ pairs of colours in different wavebands (Li et al, 2007;Li, 2013), others use narrowband continuum photometry (Rakos et al, 2007(Rakos et al, , 2008Sreedhar et al, 2012) or strength of different age-sensitive and Z-sensitive absorption line indices (Jørgensen, 1997(Jørgensen, , 1999Poggianti et al, 2001). One such set of absorption line indices was defined on the Lick/IDS system (named after the Lick Image Dissector Scanner, Faber et al, 1985).…”

Comparative Studies of Population Synthesis Models in the Framework of Modified Strömgren Filters

“…This makes the zero point of the magnitudes differ along with the cluster's redshift. (3) The flux measurement for the galaxies and the standard stars is in wavelength units (per Å), as is usual for most galaxy studies instead of frequency (per Hz) units -as in the stellar studies (Sreedhar et al 2012). These modified Strömgren filters were initially designed by Fiala et al (1986) and later used by Rakos et al (1995) to study galaxies in clusters.…”