Local Group孤立矮星系的化学史：I. dSphs：鲸鱼和杜鹃
Chemical history of isolated dwarf galaxies of the Local Group: I. dSphs: Cetus and Tucana
摘要：
首次获得了本星系群中两个孤立的矮球状星系（dSphs）杜鹃座和鲸鱼座的化学演化模型（CEMS）。CEMs是根据恒星形成历史（SFH）和金属丰度历史建立的，两者都是由LCID项目从深色星等图独立获得的。基于我们的模型，我们发现化学历史是复杂的，可以分为不同的时代和场景。特别是，在75%的SFH期间，星系表现为封闭的盒子，在剩下的25%期间，要么通过吸积获得大量原始气体，要么通过富含金属的风失去金属。为了区分这两种情况，需要老恒星的丰度比。在大约4.5 Gyr的时候，星系由于一股短而强的混合风而失去了大部分的气体。我们得到非常相似的CEMs的两个星系，虽然鲸鱼座是两倍的杜鹃座。我们的结论是，在这两个星系的恒星形成开始只有1.5%的重子质量分数预测的λ CDM。
英文摘要：
For the first time, we obtain chemical evolution models (CEMs) for Tucana and Cetus, two isolated dwarf spheroidal galaxies (dSphs) of the Local Group. The CEMs have been built from the star formation histories (SFHs) and the metallicity histories, both obtained independently by the LCID project from deep color-magnitude dia- grams. Based on our models, we find that the chemical histories were complex and can be divided into different epochs and scenarios. In particular, during 75 percent of the SFH, the galaxies behaved as closed boxes and, during the remaining 25 percent, either received a lot of primordial gas by accretion or they lost metals through metal-rich winds. In order to discriminate between these two scenarios, abundances ratios in old stars are needed. At t approximately 4.5 Gyr, the galaxies lost most of their gas due to a short-strong, well-mixed wind. We obtain very similar CEMs for both galaxies, although Cetus is twice as massive as Tucana. We conclude that the star formation in both galaxies began with only 1.5 percent of the baryonic mass fraction predicted by lambda CDM.
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