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arXiv 2103.01794astro-ph.GAgr-qc
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修正引力理论中的棒旋星系

Barred spiral galaxies in modified gravity theories

Mahmood Roshan, Indranil Banik, Neda Ghafourian, Ingo Thies, Benoit Famaey, Elena Asencio, Pavel Kroupa

摘要:

当在标准宇宙学背景下的星系形成模拟中形成棒状时,与暗物质(DM)的动力学摩擦使它们旋转得相当缓慢。然而,几乎所有观测到的星系棒都是快的,在共转半径和棒长度之间的比率。在这里,我们明确地显示了一个$8σ$张力之间的观察到的分布,这个比例,在EAGLE模拟在红移0。我们还比较了嵌入在DM晕牛顿星系盘的演变,他们的演变在三个扩展的引力理论:Milgromian动力学(MOND),非本地引力模型,和标量张量矢量引力理论(MOG)。虽然我们的模型从相同的初始重子分布和旋转曲线开始,但长期演化是不同的。与其它模型相比,MOND模型中的杆失稳现象更为严重。扩展的引力模型之间有一些共同的特征,特别是在DM模型中起关键作用的动力摩擦$-$所起的作用可以忽略不计。部分由于这个原因,所有扩展的重力模型预测较弱的酒吧和更快的酒吧模式的速度相比,DM的情况。虽然在我们的理想化,孤立的扩展重力模拟中没有强酒吧与观测紧张,他们再现了强烈的观测偏好“快”酒吧模式的速度,这是我们不能做DM。我们确认以前的研究结果,显然是'超快'酒吧可能是由于酒吧螺旋臂对齐导致高估酒吧的长度,特别是在扩展重力的情况下,酒吧已经快。

英文摘要:

When bars form within galaxy formation simulations in the standard cosmological context, dynamical friction with dark matter (DM) causes them to rotate rather slowly. However, almost all observed galactic bars are fast in terms of the ratio between corotation radius and bar length. Here, we explicitly display an $8σ$ tension between the observed distribution of this ratio and that in the EAGLE simulation at redshift 0. We also compare the evolution of Newtonian galactic discs embedded in DM haloes to their evolution in three extended gravity theories: Milgromian Dynamics (MOND), a model of non-local gravity, and a scalar-tensor-vector gravity theory (MOG). Although our models start with the same initial baryonic distribution and rotation curve, the long-term evolution is different. The bar instability happens more violently in MOND compared to the other models. There are some common features between the extended gravity models, in particular the negligible role played by dynamical friction $-$ which plays a key role in the DM model. Partly for this reason, all extended gravity models predict weaker bars and faster bar pattern speeds compared to the DM case. Although the absence of strong bars in our idealized, isolated extended gravity simulations is in tension with observations, they reproduce the strong observational preference for `fast' bar pattern speeds, which we could not do with DM. We confirm previous findings that apparently `ultrafast' bars can be due to bar-spiral arm alignment leading to an overestimated bar length, especially in extended gravity scenarios where the bar is already fast.

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