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arXiv 2005.07693astro-ph.GAastro-ph.CO
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MaNGA揭示的星系性质。III。S0s中的运动学轮廓和恒星星族梯度

Galaxy properties as revealed by MaNGA. III. Kinematic profiles and stellar population gradients in S0s

H. Domínguez Sánchez, M. Bernardi, F. Nikakhtar, B. Margalef-Bentabol, R. K. Sheth

备注：
Accepted for publication in MNRAS. 15 pages, 20 figures
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摘要：

这是第三篇文章的一系列，我们研究的恒星星族梯度（SP;年龄，金属丰度，$α$ -元素丰度比和恒星初始质量函数）的早期类型星系（ETG）在$z\le 0.08$从MANGA-DR 15调查。在这项工作中，我们专注于S 0人口和量化SP如何在整个人口以及与galactocentric距离的变化。我们通过测量Lick指数并将其与恒星星族合成模型进行比较来做到这一点。这就要求光谱具有高的信噪比，我们通过在亮度（L $_r$）和中心速度色散（$σ_0$）的箱中进行叠加来实现。我们发现：1）S 0总体存在双峰性：质量大于$3\times 10^{10}M_\odot$的S 0表现出较强的速度离散度和年龄梯度（年龄和$σ_r$向外减小），但金属丰度梯度很小或没有;而质量较小的S 0则表现出相对平坦的年龄和速度离散度剖面，但金属丰度梯度显著（即[M/H]向外减小）。高于$2\times10^{11}M_\odot$，S 0的数量急剧下降。这两个质量尺度也是ETG全球尺度关系变化的斜率。2)与具有相同亮度和速度色散的快速旋转椭圆星系（E-FR）相比，S 0的速度色散轮廓更陡。E-FR的运动学轮廓和恒星星族梯度与慢转椭圆星系（E-SR）的相似性大于S 0，表明E-FR不是简单的S 0。3）在固定的$σ_0$下，更亮的S 0和E-FR更年轻，更富金属，$α$增强更少。显然，对于这些星系，如果$σ_0$保持不变，通常的说法“大质量星系更老”是不正确的。

英文摘要：

This is the third paper of a series where we study the stellar population gradients (SP; ages, metallicities, $α$-element abundance ratios and stellar initial mass functions) of early type galaxies (ETGs) at $z\le 0.08$ from the MaNGA-DR15 survey. In this work we focus on the S0 population and quantify how the SP varies across the population as well as with galactocentric distance. We do this by measuring Lick indices and comparing them to stellar population synthesis models. This requires spectra with high signal-to-noise which we achieve by stacking in bins of luminosity (L$_r$) and central velocity dispersion ($σ_0$). We find that: 1) There is a bimodality in the S0 population: S0s more massive than $3\times 10^{10}M_\odot$ show stronger velocity dispersion and age gradients (age and $σ_r$ decrease outwards) but little or no metallicity gradient, while the less massive ones present relatively flat age and velocity dispersion profiles, but a significant metallicity gradient (i.e. [M/H] decreases outwards). Above $2\times10^{11}M_\odot$ the number of S0s drops sharply. These two mass scales are also where global scaling relations of ETGs change slope. 2) S0s have steeper velocity dispersion profiles than fast rotating elliptical galaxies (E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles and stellar population gradients of E-FRs are both more similar to those of slow rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not simply S0s viewed face-on. 3) At fixed $σ_0$, more luminous S0s and E-FRs are younger, more metal rich and less $α$-enhanced. Evidently for these galaxies, the usual statement that 'massive galaxies are older' is not true if $σ_0$ is held fixed.

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