arXiv 1609.017392016-09astro-ph.GA

EAGLE中星系的Angular momentum演化

Angular momentum evolution of galaxies in EAGLE

Claudia del P. Lagos, Tom Theuns, Adam R. H. Stevens, Luca Cortese, Nelson D. Padilla, Timothy A. Davis, Sergio Contreras, Darren Croton

备注：: 22 pages (16 without appendices). Accepted for publication in MNRAS. The only difference with previous version is a shorter abstract (to comply with the 250 words limit in MNRAS)
DOI：: 10.1093/mnras/stw2610

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摘要：

我们使用EAGLE宇宙流体动力学模拟套件来研究星系的特定角动量$j$，目的是（i）调查固定质量下$j$大范围变化背后的物理原因，以及（ii）研究简单的理论模型是否可以解释$j$演化的看似复杂和非线性的性质。我们发现，$j$的恒星，$j_{\rm stars}$，和重子，$j_{\rm bar}$，是强烈相关的恒星和重子的质量，分别与散射高度相关的形态代理，如气体分数，恒星浓度，（u-r）的固有颜色，恒星年龄和速度色散的圆速度比。我们与$z=0$的观测结果进行了比较，发现非常一致。我们发现，$j_{\rm bar}$遵循理论预期的等温塌陷晕下的特定的角动量守恒在$\approx 50$ %，而旋转支持星系的子样本同样很好地描述了一个简单的模型，其中磁盘的角动量是刚刚足以维持边缘稳定的磁盘。我们提取了EAGLE星系的恒星自旋参数演化轨迹，发现它们的$j_{\rm stars}$在$z=0$的命运敏感地依赖于它们的恒星形成和合并历史。从这些轨道，我们确定了两个不同的物理通道背后的低$j_{\rm stars}$星系在$z=0$：（i）星系合并，和（ii）早期恒星形成淬火。后者可以产生低$j_{\rm stars}$和早型形态的星系，即使在没有合并。

英文摘要：

We use the EAGLE cosmological hydrodynamic simulation suite to study the specific angular momentum of galaxies, $j$, with the aims of (i) investigating the physical causes behind the wide range of $j$ at fixed mass and (ii) examining whether simple, theoretical models can explain the seemingly complex and non-linear nature of the evolution of $j$. We find that $j$ of the stars, $j_{\rm stars}$, and baryons, $j_{\rm bar}$, are strongly correlated with stellar and baryon mass, respectively, with the scatter being highly correlated with morphological proxies such as gas fraction, stellar concentration, (u-r) intrinsic colour, stellar age and the ratio of circular velocity to velocity dispersion. We compare with available observations at $z=0$ and find excellent agreement. We find that $j_{\rm bar}$ follows the theoretical expectation of an isothermal collapsing halo under conservation of specific angular momentum to within $\approx 50$%, while the subsample of rotation-supported galaxies are equally well described by a simple model in which the disk angular momentum is just enough to maintain marginally stable disks. We extracted evolutionary tracks of the stellar spin parameter of EAGLE galaxies and found that the fate of their $j_{\rm stars}$ at $z=0$ depends sensitively on their star formation and merger histories. From these tracks, we identified two distinct physical channels behind low $j_{\rm stars}$ galaxies at $z=0$: (i) galaxy mergers, and (ii) early star formation quenching. The latter can produce galaxies with low $j_{\rm stars}$ and early-type morphologies even in the absence of mergers.

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