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arXiv 1104.4845astro-ph.CO
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椭圆星系NGC4636中有效半径为1.5的恒星运动学和星族

Stellar kinematics and populations out to 1.5 effective radius in the elliptical galaxy NGC4636

S. B. Pu, Z. Han

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14 pages, 7 figures, accepted by RAA
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摘要：

本文给出了Hobby-Eberly望远镜（HET）拍摄的大质量星系NGC 4636的长、短轴向有效半径为1.5（$R_e$）的高质量长缝光谱。利用傅里叶相关商（FCQ）方法，测量了恒星视线速度沿光轴的分布。此外，从干净的光谱中推导出六个Lick/IDS指数（$Hβ,Mgb,Fe_{5015},Fe_{5270},Fe_{5335},Fe_{5406}$）。通过比较观测到的吸收线强度与简单恒星星族（SSP）模型的预测值，得到了该星系的年龄、总金属丰度和$α$丰度分布。该星系在丰富的恒星星族之上呈现出古老和$[α/Fe]$。实际上，使用SSP模型，我们获得了宽带颜色轮廓。理论上的颜色与测量的颜色很好地匹配，并在星系中心呈现红色尖峰。颜色的尖峰主要是由星系中心的高金属丰度形成的。有趣的是，该星系有陡峭的负金属丰度梯度，但趋势是向外的。这一结果可能表明，星系的中心和外部区域是通过不同的形成过程形成的。

英文摘要：

We present high quality long slit spectra along the major and minor axes out to 1.5 effective radius ($R_e$) of the massive galaxy NGC4636 taken by Hobby-Eberly Telescope (HET). Using Fourier Correlation Quotient (FCQ) method, we measured the stellar line-of-sight velocity distribution along the axes. Furthermore, six Lick/IDS indices ($Hβ,Mgb,Fe_{5015},Fe_{5270},Fe_{5335},Fe_{5406}$) are derived from the clean spectrum. By comparing the measured absorption line strengths with the predictions of Simple Stellar Populations (SSP) models, we derived ages, total metallicity and $α$ abundance profiles of the galaxy. This galaxy presents old and $[α/Fe]$ over abundant stellar populations. Indeed, using the SSP model, we obtained the broadband color profiles. The theoretical colors match well with the measured colors and present red sharp peaks at the galaxy center. The sharp peaks of the colors are mainly shaped by the high metallicity in the galaxy center. Interestingly, the galaxy has steep negative metallicity gradients, but trend flattens outwards. This result likly suggests that the center and outer regions of the galaxy formed through different formation process.

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