Recovering stellar population parameters via different population models
  and stellar libraries
  Three basic ingredients are required to generate a simple stellar population
(SSP) library, i.e., an initial mass function (IMF), a stellar evolution
model/isochrones, and an empirical/theoretical stellar spectral library.
However, there are still some uncertainties to the determination and
understanding of these ingredients. We perform the spectral fitting to test the
relative parameter offsets between these uncertainties using two different
stellar population models, two different empirical stellar libraries, two
different isochrones, and the Salpeter and Chabrier IMFs. Based on these
setups, we select five SSP libraries generated with the Galaxev/STELIB and
Vazdekis/MILES models, and apply them to the pPXF full-spectrum fitting of both
MaNGA and mock spectra. We find that: 1) Compared to the Galaxev/STELIB model,
spectral fitting qualities with the Vazdekis/MILES model have significant
improvements for those metal-rich (especially over-solar) spectra, which cause
better reduced $\chi^2$ distributions and more precisely fitted absorption
lines. This might due to the lack of metal rich stars in the empirical STELIB
library, or code improvement of the Vazdekis model. 2) When applying the
Vazdekis/MILES model for spectral fitting, the IMF variation will lead to not
only a systematic offset in $M_*/L_r$, but also offsets in age and metallicity,
and these offsets increase with increasing stellar population ages. However,
the IMF-variation caused metallicity offsets disappear in the case of
Galaxev/STELIB based libraries. 3) The Padova2000 model provides a better match
to the MaNGA galaxy spectra at [M/H]$_L<-1.0$, while the BaSTI model match the
local galaxy spectra better at [M/H]$_L>-1.0$. Current tests suggest that
spectral fitting with the Vazdekis/MILES+BaSTI combination would be a better
choice for local galaxies.
