The mean stellar alpha-to-iron abundance ratio ([$\alpha$/Fe]) of a galaxy is an indicator of galactic star formation timescale. It is important for understanding the star formation history of early-type galaxies (ETGs) as their star formation processes have basically stopped. Using the model templates which are made by Vazdekis et al., we apply the pPXF based spectral fitting method to estimate the [$\alpha$/Fe] of 196 high signal-to-noise ratio ETGs from the MaNGA survey. The velocity dispersions within 1R$_e$ ($\sigma_{e}$) range from 27 to 270 km/s. We find a flat relation between the mean [$\alpha$/Fe] within the 1R$_e^{maj}$ ellipses and log($\sigma_{e}$), even if limiting to the massive sample with log($\sigma_{e}$/km s$^{-1}$)$>$1.9. However, the relation becomes positive after we exclude the Mg$_1$ feature in our fits, which agrees with the results from the previous work with other stellar population models, albeit with relatively large scatter. It indicates that the spectral fits with Vazdekis models could give basically the consistent predictions of [$\alpha$/Fe] with previous studies when the Mg$_b$ index is used, but do not work well at the Mg$_1$ band when their $\alpha$-enhanced version is employed in the metal-rich regime. We suggest avoiding this rather wide index, which covers 471A, as it might suffer from other effects such as flux-calibration issues. For reference, we also measure the stellar population radial gradients within 1R$_e^{maj}$ ellipses. Due to the low resolution of age estimations for old objects and the Mg$_1$ issue, the uncertainties of these gradients cannot be neglected.

中文翻译：

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SDSS-IV MaNGA：早型星系的[α/Fe]

星系的平均恒星 α 与铁丰度比 ([$\alpha$/Fe]) 是银河系恒星形成时间尺度的指标。了解早型星系 (ETG) 的恒星形成历史非常重要，因为它们的恒星形成过程已基本停止。使用 Vazdekis 等人制作的模型模板，我们应用基于 pPXF 的光谱拟合方法来估计来自 MaNGA 调查的 196 个高信噪比 ETG 的 [$\alpha$/Fe]。1R$_e$ ($\sigma_{e}$) 范围内的速度色散范围为 27 至 270 km/s。我们发现 1R$_e^{maj}$ 椭圆内的均值 [$\alpha$/Fe] 与 log($\sigma_{e}$) 之间存在平坦的关系，即使将 log($ \sigma_{e}$/km s$^{-1}$)$>$1.9。然而，在我们的拟合中排除 Mg$_1$ 特征后，关系变为正数，这与之前使用其他恒星群体模型的工作结果一致，尽管散布相对较大。这表明当使用 Mg$_b$ 指数时，与 Vazdekis 模型的光谱拟合可以给出与先前研究基本一致的 [$\alpha$/Fe] 预测，但在 Mg$_1$ 波段时效果不佳。他们的 $\alpha$ 增强版本用于富含金属的制度。我们建议避免使用这个涵盖 471A 的相当宽的索引，因为它可能会受到其他影响，例如通量校准问题。作为参考，我们还测量了 1R$_e^{maj}$ 椭圆内的恒星种群径向梯度。由于旧物体年龄估计的低分辨率和 Mg$_1$ 问题，这些梯度的不确定性不可忽视。