Mergers and the outside-in formation of dwarf spheroidals
Mergers and the outside-in formation of dwarf spheroidals
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DOI：
10.1093/mnras/stv2722
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发表时间：
2015-11
影响因子：
4.8
通讯作者：
Alejandro Ben'itez-Llambay;J. Navarro;M. Abadi;S. Gottloeber;G. Yepes;Y. Hoffman;M. Steinmetz
中科院分区：
文献类型：
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作者：
Alejandro Ben'itez-Llambay;J. Navarro;M. Abadi;S. Gottloeber;G. Yepes;Y. Hoffman;M. Steinmetz
我们使用本星系群形成的宇宙学模拟来探索矮球状星系中年龄和金属丰度梯度的起源。我们发现许多模拟的矮星是“由外而内”形成的，一个年老的、缺乏金属的人口包围着一个年轻的、更集中的富含金属的组成部分，让人想起像雕塑家或六分星这样的球状矮星。为了阐明这些梯度的起源，我们将重点放在几个例子上，其中恒星形成于年龄不同的两个种群中。两组分的空间分布反映了它们不同的起源；老恒星的组成部分是通过合并形成的，但年轻的恒星主要是原地形成的。较老的成分来自恒星形成的第一个阶段，这个阶段开始得很早，但很快就被恒星反馈和再电离的共同作用所关闭。较年轻的成分是在后期吸积事件增加气体并重新点燃恒星形成时形成的。合并的作用是分散老恒星群，增加它们的半径，降低它们相对于年轻恒星群的中心密度。我们认为，矮-矮合并为形成具有多个不同种群的系统提供了一种合理的方案，更一般地说，为矮球粒的年龄和金属丰度梯度的起源提供了一种可能。
We use a cosmological simulation of the formation of the Local Group to explore the origin of age and metallicity gradients in dwarf spheroidal galaxies. We find that a number of simulated dwarfs form "outside-in", with an old, metal-poor population that surrounds a younger, more concentrated metal-rich component, reminiscent of dwarf spheroidals like Sculptor or Sextans. We focus on a few examples where stars form in two populations distinct in age in order to elucidate the origin of these gradients. The spatial distributions of the two components reflect their diverse origin; the old stellar component is assembled through mergers, but the young population forms largely in situ. The older component results from a first episode of star formation that begins early but is quickly shut off by the combined effects of stellar feedback and reionization. The younger component forms when a late accretion event adds gas and reignites star formation. The effect of mergers is to disperse the old stellar population, increasing their radius and decreasing their central density relative to the young population. We argue that dwarf-dwarf mergers offer a plausible scenario for the formation of systems with multiple distinct populations and, more generally, for the origin of age and metallicity gradients in dwarf spheroidals.