Disentangling the stellar populations in the counter-rotating disc galaxy NGC 4550
Disentangling the stellar populations in the counter-rotating disc galaxy NGC 4550
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DOI：
10.1093/mnras/sts121
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发表时间：
2012-10
影响因子：
4.8
通讯作者：
E. Johnston;M. Merrifield;A. Aragón-Salamanca;M. Cappellari
中科院分区：
文献类型：
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作者：
E. Johnston;M. Merrifield;A. Aragón-Salamanca;M. Cappellari
为了试图了解它的起源，我们提出了高质量的长缝光谱观测的反旋转恒星盘在奇怪的S0星系NGC 4550。我们将光谱分解成两个反向旋转的恒星成分（加上一个气体成分），以研究它们的运动学和种群。推导出的运动学在很大程度上证实了以前已知的恒星盘，但跟踪它们到更大的半径，误差较小;拟合的气体成分使我们能够首次跟踪氢发射线，发现它们遵循以前在[OIII]线中看到的相同而奇怪的运动学。对这两个独立恒星组成部分的星族分析表明，次级星盘的平均年龄明显小于主星盘，这与后来由相关气体物质形成的星星相一致。此外，次级星盘更亮一些，也与这种额外的星星形成相一致。然而，这些测量不能用额外的恒星被添加到初始相同的反向旋转恒星盘的场景来自洽地建模，这排除了Evans & Collett（1994）优雅的“分界线交叉”模型，该模型用于从单个星系形成如此巨大的反向旋转盘，留下某种形式的不寻常的气体吸积历史作为最可能的形成机制。
In order to try and understand its origins, we present high-quality long-slit spectral observations of the counter-rotating stellar discs in the strange S0 galaxy NGC 4550. We kinematically decompose the spectra into two counter-rotating stellar components (plus a gaseous component), in order to study both their kinematics and their populations. The derived kinematics largely confirm what was known previously about the stellar discs, but trace them to larger radii with smaller errors; the fitted gaseous component allows us to trace the hydrogen emission lines for the first time, which are found to follow the same rather strange kinematics previously seen in the [OIII] line. Analysis of the populations of the two separate stellar components shows that the secondary disc has a significantly younger mean age than the primary disc, consistent with later star formation from the associated gaseous material. In addition, the secondary disc is somewhat brighter, also consistent with such additional star formation. However, these measurements cannot be self-consistently modelled by a scenario in which extra stars have been added to initially-identical counter-rotating stellar discs, which rules out Evans & Collett's (1994) elegant "separatrix-crossing" model for the formation of such massive counter-rotating discs from a single galaxy, leaving some form of unusual gas accretion history as the most likely formation mechanism.