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For refcode 2000ApJ...532..193F:
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Copyright by American Astronomical Society. Reproduced by permission
2000ApJ...532..193F Probing the Evolution of Early-Type Cluster Galaxies through Chemical Enrichment Ignacio Ferreras and Joseph Silk Nuclear and Astrophysics Laboratory, 1 Keble Road, Oxford OX1 3RH, UK; ferreras@astro.ox.ac.uk, silk@astro.ox.ac.uk Received 1999 May 12; accepted 1999 November 3 ABSTRACT We describe a simple chemical enrichment model for cluster early-type galaxies, in which the main mechanisms considered in the evolutionary model are infall of primordial gas, outflows, and a possible variation in the star formation efficiency. We find that-within the framework of our models- only outflows can generate the suitable range of metallicities needed in order to explain the color-magnitude relation. The chemical enrichment tracks can be combined with the latest population synthesis models from Bruzual & Charlot to simulate clusters over a wide redshift range, for a set of toy models with different infall rates, star formation efficiencies, and star formation scenarios. The color-magnitude relation of local clusters is used as a constraint, fixing the correlation between absolute luminosity and the ejected fraction of gas from outflows. We find that the correlations between color or mass-to-light ratios and absolute luminosity are degenerate with respect to most of the input parameters. However, a significant change between monolithic and hierarchical models is predicted for redshifts z >~ 1. The most important observable that differentiates between these alternative formation scenarios is the population of blue early-type galaxies that fall conspicuously blueward of the red envelope. The comparison between predicted and observed mass-to-light ratios yields an approximate linear bias between total and stellar masses, M_tot_ is proportional to M_st_^1.15+/-0.08^, in early-type galaxies. If we assume that outflows constitute the driving mechanism for the colors observed in cluster early-type galaxies, the metallicity of the intracluster medium (ICM) can be linked to outflows; the color-magnitude constraint requires faint (M_V) ~ -16) galaxies to eject 85% of their gas, which means that most of the metals in the ICM may have originated in these dwarf galaxies. No significant evolution is predicted, in agreement with X-ray observations by Mushotzky & Loewenstein. Other mechanisms contributing to the enrichment of the ICM, such as ejected material from mergers that formed the largest ellipticals, should translate into a decrease of the intracluster metallicity at z >~ 1-1.5. Forthcoming observations from Chandra and XMM will help elucidate this point. Subject headings: galaxies: clusters: general-galaxies: elliptical and lenticular, cD-galaxies: evolution-galaxies: formation -galaxies: photometry-galaxies: stellar content
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