Using the final MaNGA sample (DR17) of 10K galaxies, we investigate the dark matter fraction $f_{\rm DM}$ within one half-light radius $R_{\rm e}$ for about 6K galaxies with good kinematics spanning a wide range of morphologies and stellar velocity dispersion ($1.6\lesssim \lg\,\sigma_{\rm e}/\mathrm{km\,s^{-1}}\lesssim 2.6$). We employ two techniques to estimate $f_{\rm DM}$: (i) Jeans Anisotropic Modelling (JAM), which performs dark matter decomposition based on the stellar kinematics and (ii) comparing the total dynamical mass-to-light ratios $(M/L)_{\rm JAM}$ and the $(M_{\ast}/L)_{\rm SPS}$ from Stellar Population Synthesis (SPS). We find that both methods consistently show a significant trend of increasing $f_{\rm DM}$ with decreasing $\sigma_{\rm e}$, for $\lg(\sigma_{\rm e}/\mathrm{km\,s^{-1}})\lesssim2.1$ and very low $f_{\rm DM}$ at larger $\sigma_{\rm e}$. For the 235 early-type galaxies with the best dynamical models, we explore the variation of the stellar initial mass function (IMF) by comparing the stellar mass-to-light ratios $(M_{\ast}/L)_{\rm JAM}$ from JAM and SPS. We confirm that the stellar mass excess $\alpha_{\rm IMF}\equiv (M_{\ast}/L)_{\rm JAM}/(M_{\ast}/L)_{\rm SPS}$, which reflects the IMF shape, increases with $\sigma_{\rm e}$, in agreement with previous studies that reported a transition from Chabrier-like to Salpeter IMF among galaxies. We also detect weak positive correlations between $\alpha_{\rm IMF}$ and age, but no correlations with metallicity ($[Z/H]$). Finally, we stack galaxy spectra according to their $\alpha_{\rm IMF}$ to search for differences in IMF-sensitive spectral features (e.g. the $\rm Na_{\rm I}$ doublet). We only find marginal evidence for such differences, which casts doubt on the validity of one or both methods to measure the IMF.
Comment: 17 pages, 9 figures, 2 tables; Submitted to MNRAS on 21 September 2023