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首页> 外文期刊>The Astrophysical journal >The Ages of Dwarf Elliptical Galaxies
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The Ages of Dwarf Elliptical Galaxies

机译:矮椭圆星系的时代

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We present narrowband photometry of 91 dwarf elliptical galaxies in the Coma and Fornax Clusters taken with the Str?mgren (uvby) filter system. Dividing the sample by dwarf morphology into nucleated (dEN) and nonnucleated (dE) dwarfs reveals two distinct populations of early-type systems based on integrated colors. The class of dEN galaxies are redder in their continuum colors as compared to bright cluster ellipticals and dE type dwarfs, and their position in multicolor diagrams can only be explained by an older mean age for their underlying stellar populations. By comparison with the narrowband photometry of the M87 globular cluster system, we find that dEN's are a higher metallicity continuation of the old, metal-poor color sequence of galactic globular clusters and the blue population of M87 globular clusters. Bright ellipticals and dE dwarfs, on the other hand, follow the color sequence of the metal-rich, red population of M87 globular clusters. A comparison to SED models, convolved to a simple metallicity model, finds that dEN's and blue globular clusters are 3 to 4 Gyr older than cluster ellipticals and 5 Gyr older than dE type galaxies. The implication is that globular clusters and dEN galaxies are primordial and have metallicities set by external constraints such as the enrichment of their formation clouds. Bright ellipticals and dE galaxies have metallicities and ages that suggest an extended phase of initial star formation that produces a younger mean age, even if their formation epoch is similar to that of dEN's and blue globular clusters, and an internally driven chemical evolutionary history.
机译:我们用Str?mgren(uvby)滤镜系统对91个矮彗星和Fornax星团中的椭圆椭圆星系进行窄带测光。将样本按矮小形态分为有核的(dEN)和无核的(dE)矮人,可以发现两种基于集成色的不同的早期类型系统。与明亮的簇椭圆形和dE型矮星相比,dEN星系的连续体颜色更红,并且它们在多色图中的位置只能由其潜在恒星群体的平均年龄高来解释。通过与M87球状星团系统的窄带光度法进行比较,我们发现dEN是银质球状星团的旧的,金属贫乏的颜色序列和M87球状星团的蓝色种群的更高金属性延续。另一方面,明亮的椭圆形和dE矮形遵循M87球状簇中富含金属的红色群体的颜色顺序。与SED模型的比较(转为简单的金属性模型)发现,dEN和蓝色球状星团比椭圆形星团大3至4 Gyr,比dE型星系大5 Gyr。这意味着球状星团和dEN星系是原始的,并具有由外部约束(例如,它们的形成云的富集)设定的金属性。明亮的椭圆形和dE星系具有金属性和年龄,这表明初始恒星形成的延长阶段会产生更年轻的平均年龄,即使它们的形成时期与dEN和蓝色球状星团的形成时期相似,并且是内部驱动的化学演化历史。

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