A possible solution to the [a/Fe]-s problem in early-type galaxies within a hierarchical galaxy formation model The [a/Fe]-s problem in early-type galaxies
A possible solution to the [a/Fe]-s problem in early-type galaxies within a hierarchical galaxy formation model The [a/Fe]-s problem in early-type galaxies
复制标题
分层星系形成模型中早期型星系中 [a/Fe]-s 问题的一种可能解决方案 早期型星系中的 [a/Fe]-s 问题
DOI：
10.1111/j.1745-3933.2011.01017.x
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Calura F
中科院分区：
文献类型：
--
作者：
Calura F
质量最大的椭圆星系显然形成得最快，因为α元素（如氧）与铁的比例最小。事实上，铁主要来自Ia型超新星，时间尺度为10.1 -1 Byr，而α元素则来自大质量恒星，时间尺度为数千万年。对于星系形成的宇宙学理论来说，再现这样的α/Fe相关性一直是一个严重的问题，这些理论设想大质量星系是从较小的祖先逐渐聚集起来的，并且以星星形成历史向宇宙晚期过度延伸为特征。虽然最近已经清楚，活动星系核（AGN）活动的反馈在星星形成的晚期淬灭中起着一定的作用，并且星系祖先中早期的星星形成历史会影响α/Fe比，但单靠大合并并不能将高红移祖先中的星星形成提高到与观测到的α/Fe相关性的陡度相匹配的水平。在这里，我们报告说，包括飞行的“骚扰”的影响，触发较低级别的星暴，结合AGN淬火的星暴活动，大大提高了能力，占观测到的α/Fe比在宇宙学星系形成模型中的椭圆。早期的工作和目前的结果之间的关键区别是由飞掠碰撞驱动的恒星爆发的影响，这在大质量星系的高红移祖先中是非常常见的，并且在大爆炸后的前2亿年内促进了星星的形成，结合了前3-4 Gyr内爆发活动的淬灭。
The most massive elliptical galaxies apparently formed the fastest, because the ratio of α elements (such as oxygen) to iron is the smallest. In fact, iron is mainly produced from type Ia supernovae on a time-scale of ∼0.1–1 Byr, while the α elements come from massive stars on time-scales of a few tens of million years. Reproducing such a α/Fe correlation has long been a severe problem for cosmological theories of galaxy formation, which envisage massive galaxies to assemble gradually from smaller progenitors, and to be characterized by a star formation history too much extended towards late cosmic times. While it has recently become clear that feedback from Active Galactic Nuclei (AGNs) activity plays a role in the late quenching of star formation, and that early star formation history in the galaxy progenitors affect the α/Fe ratio, major mergers alone cannot enhance the star formation in the high-redshift progenitors to the levels required to match the steepness of the observed α/Fe correlation. Here we report that the inclusion of the effects of fly-by ‘harassments’, that trigger lower level starbursts, combined with the AGN quenching of the starburst activity, considerably enhances the capability to account for the observed α/Fe ratio in ellipticals within cosmological galaxy formation models. The critical difference between the earlier work and the present result is the effect of starbursts driven by fly-by encounters that would have been very common amongst the high-redshift progenitors of massive galaxies and which would have boosted star formation in the first 2 Byr after the big bang, combined with quenching of the burst activity within the first 3–4 Gyr.