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arXiv 1805.04443astro-ph.GA
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絮凝螺旋M33的模拟：是什么驱动了螺旋结构？

Simulations of the flocculent spiral M33: what drives the spiral structure?

C. L. Dobbs, A. R. Pettitt, E. Corbelli, J. E. Pringle

备注：
17 pages, 17 figures, accepted for publication in MNRAS
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摘要：

我们进行模拟孤立的星系，以调查可能的起源的螺旋结构在M33。在我们的模型中，我们发现恒星和气体中的引力不稳定性能够再现在HI中观察到的M33的螺旋图案和速度场，并且不需要相互作用。我们还发现，最佳模型具有高水平的恒星反馈，这会产生类似于在M33中观察到的大洞，而较低水平的反馈往往会产生大量的小尺度结构，以及不受干扰的高表面密度气体长纤维，在M33盘中几乎检测不到。气体成分似乎在产生这种结构中起着重要的作用，所以如果没有什么反馈，气体和恒星都会组织成清晰的旋臂，这可能是由于较低的组合$Q$（使用气体和恒星），以及冷气体容易经历螺旋冲击的能力。相比之下，具有更高反馈的模型具有更弱的螺旋结构，特别是在恒星部分，与大设计星系相比。然而，我们没有看到$Q_{stars}$在这些模型中的行为有很大的差异，因为$Q_{stars}$保持相对恒定，除非椎间盘更不稳定。我们的模型表明，虽然恒星产生了一些潜在的螺旋结构，这是相对较弱的，气体物理在生产的大尺度结构的絮凝螺旋ISM相当大的作用。

英文摘要：

We perform simulations of isolated galaxies in order to investigate the likely origin of the spiral structure in M33. In our models, we find that gravitational instabilities in the stars and gas are able to reproduce the observed spiral pattern and velocity field of M33, as seen in HI, and no interaction is required. We also find that the optimum models have high levels of stellar feedback which create large holes similar to those observed in M33, whilst lower levels of feedback tend to produce a large amount of small scale structure, and undisturbed long filaments of high surface density gas, hardly detected in the M33 disc. The gas component appears to have a significant role in producing the structure, so if there is little feedback, both the gas and stars organise into clear spiral arms, likely due to a lower combined $Q$ (using gas and stars), and the ready ability of cold gas to undergo spiral shocks. By contrast models with higher feedback have weaker spiral structure, especially in the stellar component, compared to grand design galaxies. We did not see a large difference in the behaviour of $Q_{stars}$ with most of these models, however, because $Q_{stars}$ stayed relatively constant unless the disc was more strongly unstable. Our models suggest that although the stars produce some underlying spiral structure, this is relatively weak, and the gas physics has a considerable role in producing the large scale structure of the ISM in flocculent spirals.

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