Massive spheroids can form in single minor mergers
Massive spheroids can form in single minor mergers
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DOI：
10.1093/mnras/stz2440
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发表时间：
2019-09
影响因子：
4.8
通讯作者：
Ryan A. Jackson;G. Martin;S. Kaviraj;C. Laigle;J. Devriendt;Y. Dubois;C. Pichon
中科院分区：
文献类型：
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作者：
Ryan A. Jackson;G. Martin;S. Kaviraj;C. Laigle;J. Devriendt;Y. Dubois;C. Pichon
了解旋转支撑盘如何转变为弥散主导的球体是我们理解星系演化的核心。形态转换主要是由合并驱动的。虽然大合并可以有效地创建球状体，最近的工作突出了其他过程的重要作用，如小合并，在驱动形态变化。鉴于它们丰富的合并历史，球状体通常表现出大部分的“非原位”恒星质量，即通过合并从外部物体吸积的质量。对于质量最大的星系来说尤其如此，它们的恒星质量通常不可能在没有大量合并的情况下达到。在这里，我们探索了一个不寻常的人口极其巨大的（M* > 1011 M）的球状体，在地平线AGN模拟，表现出异常低的异位质量分数，表明它们的形成没有诉诸于重大合并。这些系统形成于一个单一的小合并事件（典型的合并质量比为0.11-0.33），具有特定的轨道配置，卫星轨道几乎与大质量星系的圆盘共面。合并引发了一场灾难性的形态变化，仅仅几百万年，伴随着强烈的原地星星形成。虽然这条通道产生了少数（15%）这样的星系，但我们的研究表明，至少有一些最大质量的球状体的形成不需要涉及重大合并-或任何重大合并-与经典的看法相反。
Understanding how rotationally supported discs transform into dispersion-dominated spheroids is central to our comprehension of galaxy evolution. Morphological transformation is largely merger-driven. While major mergers can efficiently create spheroids, recent work has highlighted the significant role of other processes, like minor mergers, in driving morphological change. Given their rich merger histories, spheroids typically exhibit large fractions of ‘ex situ’ stellar mass, i.e. mass that is accreted, via mergers, from external objects. This is particularly true for the most massive galaxies, whose stellar masses typically cannot be attained without a large number of mergers. Here, we explore an unusual population of extremely massive (M* > 1011M⊙) spheroids, in the Horizon-AGN simulation, which exhibit anomalously low ex situ mass fractions, indicating that they form without recourse to significant merging. These systems form in a single minor-merger event (with typical merger mass ratios of 0.11–0.33), with a specific orbital configuration, where the satellite orbit is virtually co-planar with the disc of the massive galaxy. The merger triggers a catastrophic change in morphology, over only a few hundred Myr, coupled with strong in situ star formation. While this channel produces a minority (∼5 per cent) of such galaxies, our study demonstrates that the formation of at least some of the most massive spheroids need not involve major mergers – or any significant merging at all – contrary to what is classically believed.