Geometric properties of galactic discs with clumpy episodes
Geometric properties of galactic discs with clumpy episodes
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DOI：
10.1093/mnras/staa065
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发表时间：
2019-11
影响因子：
4.8
通讯作者：
L. B. E. Silva;V. Debattista;T. Khachaturyants;D. Nidever
中科院分区：
文献类型：
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作者：
L. B. E. Silva;V. Debattista;T. Khachaturyants;D. Nidever
最近提出了在银河系化学空间[α/Fe]与[Fe/H]中形成双模态的设想，其中α-增强恒星在团块中早期和快速地产生。除了加速α-元素在介质中的富集外，这些团块还分散了老恒星，将平面内运动转化为垂直运动，形成了一个几何厚盘。在本文中，通过对光滑颗粒流体动力学模拟数据的详细分析，我们研究了在这种情况下产生的几何性质（特别是化学厚盘）。对于单年龄星群，我们证明了高[α/Fe]星的表面径向密度分布可以用单指数很好地描述，而低[α/Fe]星的表面径向密度分布则需要破指数。这一差距对年轻人来说很明显，对老年人来说更大。断口的位置与年龄无关。单年龄星群的垂直密度分布具有单指数特征，低[α/Fe]星的密度分布明显，而高[α/Fe]星的密度分布微弱（或根本没有）。对于低[α/Fe]恒星，随着年龄的增长，耀斑水平降低，而对于高[α/Fe]恒星，耀斑水平随着年龄的增长而微弱增加（尽管有很大的不确定性）。所有这些特性都与最近报道的银河系的观测结果一致，使这成为银河系厚盘形成的一个可信的场景。
A scenario for the formation of the bi-modality in the chemical space [α/Fe] versus [Fe/H] of the Milky Way was recently proposed in which α-enhanced stars are produced early and quickly in clumps. Besides accelerating the enrichment of the medium with α-elements, these clumps scatter the old stars, converting in-plane to vertical motion, forming a geometric thick disc. In this paper, by means of a detailed analysis of the data from smooth particle hydrodynamical simulations, we investigate the geometric properties (in particular of the chemical thick disc) produced in this scenario. For mono-age populations we show that the surface radial density profiles of high-[α/Fe] stars are well described by single exponentials, while that of low-[α/Fe] stars require broken exponentials. This break is sharp for young populations and broadens for older ones. The position of the break does not depend significantly on age. The vertical density profiles of mono-age populations are characterized by single exponentials, which flare significantly for low-[α/Fe] stars but only weakly (or not at all) for high-[α/Fe] stars. For low-[α/Fe] stars, the flaring level decreases with age, while for high-[α/Fe] stars it weakly increases with age (although with large uncertainties). All these properties are in agreement with observational results recently reported for the Milky Way, making this a plausible scenario for the formation of the Galactic thick disc.