The origin of discs and spheroids in simulated galaxies
The origin of discs and spheroids in simulated galaxies
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DOI：
10.1111/j.1365-2966.2012.20975.x
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发表时间：
2011-12
影响因子：
4.8
通讯作者：
L. Sales;J. Navarro;T. Theuns;J. Schaye;S. White;C. Frenk;R. Crain;C. D. Vecchia
中科院分区：
文献类型：
--
作者：
L. Sales;J. Navarro;T. Theuns;J. Schaye;S. White;C. Frenk;R. Crain;C. D. Vecchia
星系的主要形态特征被认为是由其周围暗晕的组装历史和净自旋决定的。在最简单的情况下，盘星系主要形成在具有高角动量和安静的最近组装历史的晕中，而球状体是重复合并事件的缓慢旋转残余物。我们探索这些假设使用100个系统的晕质量类似于银河系，在一系列宇宙学气体动力学模拟：银河系星系际介质相互作用计算（GIMIC）。在z=0时，模拟的星系表现出各种各样的形态，从分散为主的球状体到纯盘星系。令人惊讶的是，这些形态特征与它们的晕特性相关性很差：圆盘形成于具有高和低净自旋的晕中，并且合并在球状体的形成中起着可以忽略不计的作用，球状体的恒星主要在原位形成。事后看来，晕和星系性质之间的这种弱相关性并不令人惊讶，因为少数可用的重子（约40%）最终会出现在星系中。对形态学更重要的是，随着时间的推移，重子吸积形成星系的角动量的相干排列。当新吸积气体的自旋与现存星系的自旋不一致时，球状体倾向于形成，导致具有不同运动学的恒星的阶段性形成，抵消了系统的净旋转。另一方面，圆盘是由气体形成的，这些气体以与早期吸积物质相似的角动量流入。来自热日冕的气体吸积因此有利于盘的形成，而“冷”流动的气体，通常沿着分离的、错位的细丝，有利于球状体的形成。在这种情况下，许多球状体由具有不同运动学、年龄和金属丰度的恒星成分叠加而成，这种排列可能会一直延续到今天，因为缺乏重大的合并。由于角动量主要是在转向时获得的，因此形态取决于潮汐场和注定形成星系的物质形状之间的早期相互作用。
The major morphological features of a galaxy are thought to be determined by the assembly history and net spin of its surrounding dark halo. In the simplest scenario, disc galaxies form predominantly in haloes with high angular momentum and quiet recent assembly history, whereas spheroids are the slowly rotating remnants of repeated merging events. We explore these assumptions using 100 systems with halo masses similar to that of the Milky Way, identified in a series of cosmological gasdynamical simulations: the Galaxies–Intergalactic Medium Interaction Calculation (GIMIC). At z=0, the simulated galaxies exhibit a wide variety of morphologies, from dispersion-dominated spheroids to pure disc galaxies. Surprisingly, these morphological features are very poorly correlated with their halo properties: discs form in haloes with high and low net spin, and mergers play a negligible role in the formation of spheroids, whose stars form primarily in situ. With hindsight, this weak correlation between halo and galaxy properties is unsurprising given that a minority of the available baryons (∼40 per cent) end up in galaxies.More important to morphology is the coherent alignment of the angular momentum of baryons that accrete over time to form a galaxy. Spheroids tend to form when the spin of newly accreted gas is misaligned with that of the extant galaxy, leading to the episodic formation of stars with different kinematics that cancel out the net rotation of the system. Discs, on the other hand, form out of gas that flows in with similar angular momentum to that of earlier accreted material. Gas accretion from a hot corona thus favours disc formation, whereas gas that flows ‘cold’, often along separate, misaligned filaments, favours the formation of spheroids. In this scenario, many spheroids consist of the superposition of stellar components with distinct kinematics, age and metallicity, an arrangement that might survive to the present day given the paucity of major mergers. Since angular momentum is acquired largely at turnaround, morphology depends on the early interplay between the tidal field and the shape of the material destined to form a galaxy.