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Register a new userThe Gemini/HST Galaxy Cluster Project: Stellar Populations in the Low Redshift Reference Cluster Galaxies
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Inger Jorgensen
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In order to study stellar populations and galaxy structures at intermediate and high redshift (z=0.2-2.0) and link these properties to those of low redshift galaxies, there is a need for well-defined local reference samples. Especially for galaxies in massive clusters, such samples are often limited to the Coma cluster galaxies. We present consistently calibrated velocity dispersions and absorption line indices for galaxies in the central 2 R500 x 2 R500 of four massive clusters at z<0.1: Abell 426/Perseus, Abell 1656/Coma, Abell 2029, and Abell 2142. The measurements are based on data from Gemini Observatory, McDonald Observatory, and the Sloan Digital Sky Survey. For bulge-dominated galaxies the samples are 95 percent complete in Perseus and Coma, and 74 percent complete in A2029 and A2142, to a limit of M_Babs <= -18.5 mag. The data serve as the local reference for our studies of galaxy populations in the higher redshift clusters that are part of the Gemini/HST Galaxy Cluster Project (GCP). We establish the scaling relations between line indices and velocity dispersions as reference for the GCP. We derive stellar population parameters ages, metallicities [M/H], and abundance ratios from line indices, both averaged in bins of velocity dispersion, and from individual measurements for galaxies in Perseus and Coma. The zero points of relations between the stellar population parameters and the velocity dispersions limit the allowed cluster-to-cluster variation of the four clusters to +-0.08 dex in age, +-0.06 dex in [M/H], +-0.07 dex in [CN/Fe], and +-0.03 dex in [Mg/Fe].
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We present detailed, high spatial and spectral resolution, long-slit observations of four central cluster galaxies (Abell 0085, 0133, 0644 and Ophiuchus) recently obtained on the Southern African Large Telescope (SALT). Our sample consists of central cluster galaxies (CCGs) with previously-observed Halpha-filaments, and have existing data from the X-ray to radio wavelength regimes available. Here, we present the detailed optical data over a broad wavelength range to probe the spatially-resolved kinematics and stellar populations of the stars. We use the Pegase.HR model with the ELODIE v3.1 stellar library to determine the star formation histories of the galaxies using full spectrum fitting. We perform single stellar population (SSP) as well as composite stellar population (CSP) fits to account for more complex star formation histories. Monte-Carlo simulations and chi 2-maps are used to check the reliability of the solutions. This, combined with the other multiwavelength data, will form a complete view of the different phases (hot and cold gas and stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters, as well as the influence of the host cluster. We find small, young stellar components in at least three of the four galaxies, even though two of the three host clusters have zero spectrally-derived mass deposition rates from X-ray observations.
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