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arXiv 1607.01290astro-ph.GA
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当场捕获:在屈曲阶段直接探测银河棒

Caught in the Act: Direct Detection of Galactic Bars in the Buckling Phase

Peter Erwin, Victor P. Debattista

摘要:

大多数大质量盘状星系,包括我们自己的星系,都有垂直厚的内部区域的恒星棒-所谓的“盒子/花生形”(B/P)凸起。最常见的B/P凸起的形成机制是棒中剧烈的垂直“屈曲”不稳定性,这在N体模拟中已经出现了20多年,但从未在真实星系中发现。在这里,我们提出了两个邻近星系(NGC 3227和NGC 4569)正在进行的屈曲的第一个直接观测证据,包括特征不对称等照度线和(在NGC 4569中)与模拟屈曲相匹配的恒星运动学不对称性。这证实了在真实星系中发生了屈曲不稳定性并产生了B/P凸起。如果屈曲阶段持续~0.5--1 Gyr,则杆演化的玩具模型产生与观测一致的屈曲杆局部分数,与模拟一致。

英文摘要:

The majority of massive disk galaxies, including our own, have stellar bars with vertically thick inner regions -- so-called "boxy/peanut-shaped" (B/P) bulges. The most commonly suggested mechanism for the formation of B/P bulges is a violent vertical "buckling" instability in the bar, something that has been seen in N-body simulations for over twenty years, but never identified in real galaxies. Here, we present the first direct observational evidence for ongoing buckling in two nearby galaxies (NGC 3227 and NGC 4569), including characteristic asymmetric isophotes and (in NGC 4569) stellar-kinematic asymmetries that match buckling in simulations. This confirms that the buckling instability takes place and produces B/P bulges in real galaxies. A toy model of bar evolution yields a local fraction of buckling bars consistent with observations if the buckling phase lasts ~0.5--1 Gyr, in agreement with simulations.

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