论文标题

两次大规模早期积聚事件在类似银河系的星系中的影响:积累恒星碟和光晕的影响

The impact of two massive early accretion events in a Milky Way-like galaxy: repercussions for the buildup of the stellar disc and halo

论文作者

Orkney, Matthew D. A., Laporte, Chervin F. P., Grand, Robert J. J., Gómez, Facundo A., van de Voort, Freeke, Marinacci, Federico, Pakmor, Ruediger, Springel, Volker

论文摘要

我们从Auriga模拟中确定并表征了带有两个连续的大规模合并$ \ sim2 \,$ gyr的Auriga模拟,在高红移处与$ GYR相距,可与报道的Kraken和Gaia-Sausage-Ecceladus相当。类似Kraken的合并($ z = 1.6 $,$ m _ {\ rm tot} = 8 \ times10^{10} \,$ m $ _ {\ odot} $)是富含气体的,它的大部分质量都沉积在$ 10 \,$ 10 \,$ kpc中,并且是很大程度的同位素。类似香肠的合并($ z = 1.14 $,$ m _ {\ rm tot} = 1 \ times10^{11} \,$ m $ _ {\ odot} $)在较高的能量上留下了更扩展的质量分布,并且具有径向的偏分配。对于较高的红移合并,卫星与托管星系的恒星质量比为1:3。结果,残留物的化学与同时的原位人群没有区别,这使得通过化学丰度确定该组成部分变得具有挑战性。这很自然地解释了为什么迄今为止将所有丰度模式归因于Kraken,实际上与金属贫困的原位所谓的Aurora种群和厚盘完全一致。但是,我们的模型做出了可伪造的预测:如果银河系在高红移时进行了富含气体的双重合并,则应将其烙印在其恒星形成历史上,爆发约为$ \ sim2 \,$ $ gyrs。这可能会在最高降低的主要合并中提供约束功率。

We identify and characterise a Milky Way-like realisation from the Auriga simulations with two consecutive massive mergers $\sim2\,$Gyr apart at high redshift, comparable to the reported Kraken and Gaia-Sausage-Enceladus. The Kraken-like merger ($z=1.6$, $M_{\rm Tot} = 8\times10^{10}\,$M$_{\odot}$) is gas-rich, deposits most of its mass in the inner $10\,$kpc, and is largely isotropic. The Sausage-like merger ($z=1.14$, $M_{\rm Tot} = 1\times10^{11}\,$M$_{\odot}$) leaves a more extended mass distribution at higher energies, and has a radially anisotropic distribution. For the higher redshift merger, the stellar mass ratio of the satellite to host galaxy is 1:3. As a result, the chemistry of the remnant is indistinguishable from contemporaneous in-situ populations, making it challenging to identify this component through chemical abundances. This naturally explains why all abundance patterns attributed so far to Kraken are in fact fully consistent with the metal-poor in-situ so-called Aurora population and thick disc. However, our model makes a falsifiable prediction: if the Milky Way underwent a gas-rich double merger at high redshift, then this should be imprinted on its star formation history with bursts about $\sim2\,$Gyrs apart. This may offer constraining power on the highest-redshift major mergers.

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