Galaxy Populations and Evolution in Clusters. III. The Origin of Low-Mass Galaxies in Clusters: Constraints from Stellar Populations

Abstract

Low-mass galaxies in nearby clusters are the most numerous galaxy type in the universe, yet their origin and properties remain largely unknown. To study basic questions concerning these galaxies we present the results of a survey designed to constrain the characteristics and properties of the stellar populations in a magnitude complete sample of low-mass cluster galaxies (LMCGs) in the center of the Perseus cluster. Using deep, high-quality WIYN UBR images, we demonstrate that the 53 LMCGs in our sample have a significant scatter about the color-magnitude relationship at M_B > -15. By comparing single-burst stellar population models to our photometry, we argue that stellar populations in LMCGs all have ages > 1 Gyrs, with redder LMCGs having stellar metallicities [Fe/H] > -0.5. By assuming that the colors of LMCGs reflect metallicity, and have co-evolved with the giant ellipticals, we find a wide range of values, from solar to [Fe/H] ~ -3. We argue from this that LMCGs have multiple origins, and fundamentally differ from Local Group dwarf spheroidals/ellipticals. The inferred lower metallicities of the bluer LMCGs implies that these are possibly primordial galaxies formed through self enrichment and stellar feedback provided by winds from supernova. We also investigate several other formation scenarios for these LMCGS, including: self enrichment induced by the confinement of metals in halos by the intracluster medium, in situ formation out of intracluster gas, systems with extreme dark halos, and as remnants of higher mass systems. We conclude that roughly half of all low-mass cluster galaxies have stellar populations and kinematic properties, discussed in previous papers in this series, consistent with being the remnants of stripped galaxies accreted into clusters a few Gyrs ago.Comment: Accepted to the Astronomical Journal, 35 pages. For full resolution images of the cluster LMCGs and other figures, please download the version at http://www.astro.caltech.edu/~cc/gpec3.p