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 Vazdekis models have self-inconsistency and do not actually cover the observations in Mg _ { 1 } .
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 can not be neglected .