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arXiv 1610.04516astro-ph.GA
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主导暗物质和反向旋转盘:低光度S0星系NGC 5102的MUSE视图

Dominant dark matter and a counter rotating disc: MUSE view of the low luminosity S0 galaxy NGC 5102

Martin Mitzkus, Michele Cappellari, C. Jakob Walcher

摘要:

利用多单元光谱探测器(MUSE)的积分场谱研究了低质量近邻S 0星系NGC 5102的运动学和恒星星族。运动学图首次揭示了NGC 5102具有特征2 sigma峰,表明星系具有反向旋转盘。通过将两个运动学分量拟合到观测到的光谱,定量地证实了这种解释。通过恒星星族分析,我们确认了已知的年轻恒星星族在中心,并发现陡峭的年龄和金属丰度梯度。我们构造了恒星动力学的轴对称Jeans各向异性模型,研究了星系的初始质量函数(IMF)和暗物质晕。模型显示,这个星系与以前用类似方法研究的所有星系都有很大不同:即使在半光半径内,它也不能用自洽的质量跟随光假设来近似。考虑到NFW暗物质晕,我们需要一个重IMF和一个有效半径的球体内的暗物质分数为0.37 ± 0.04来描述恒星运动学。具有自由斜率的暗物质晕的更一般的模型显示斜率和IMF是退化的,但是表明具有更陡(收缩)晕的轻质IMF(Chabrier样)和更高的暗物质分数更好地拟合数据。不管关于晕轮廓的假设如何,我们测量总质量密度的斜率为-1.75+-0.04。这比等温晕的-2斜率要浅,也比已发表的大质量早期星系的斜率要浅。

英文摘要:

The kinematics and stellar populations of the low-mass nearby S0 galaxy NGC 5102 are studied from integral field spectra taken with the Multi-Unit Spectroscopic Explorer (MUSE). The kinematic maps reveal for the first time that NGC 5102 has the characteristic 2 sigma peaks indicative of galaxies with counter-rotating discs. This interpretation is quantitatively confirmed by fitting two kinematic components to the observed spectra. Through stellar population analysis we confirm the known young stellar population in the centre and find steep age and metallicity gradients. We construct axisymmetric Jeans anisotropic models of the stellar dynamics to investigate the initial mass function (IMF) and the dark matter halo of the galaxy. The models show that this galaxy is quite different from all galaxies previously studied with a similar approach: even within the half-light radius, it cannot be approximated with the self-consistent mass-follows-light assumption. Including an NFW dark matter halo, we need a heavy IMF and a dark matter fraction of 0.37+-0.04 within a sphere of one effective radius to describe the stellar kinematics. The more general model with a free slope of the dark matter halo shows that slope and IMF are degenerate, but indicates that a light weight IMF (Chabrier-like) and a higher dark matter fraction, with a steeper (contracted) halo, fit the data better. Regardless of the assumptions about the halo profile, we measure the slope of the total mass density to be -1.75+-0.04. This is shallower than the slope of -2 of an isothermal halo and shallower than published slopes for more massive early type galaxies.

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