2020MNRAS.495.4820L

Galaxy properties are known to correlate most tightly with the galaxy effective stellar velocity dispersion σ_e. Here, we look for additional trends at fixed σ_e using 1339 galaxies (M_* >= 6 x 10⁹ M_☉) with different morphologies in the MaNGA (DR14) sample with integral-field spectroscopy data. We focus on the gradients (γ_rms ≡ σ(R_e/4)/σ_e) of the stellar root-mean-square velocity (V_ rms_ ≡sqrt(V²+σ²)), which we show traces the total mass density gradient γ_tot derived from dynamical models and, more weakly, the bulge fraction. We confirm that γ_rms increases with σ_e, age, and metallicity. We additionally find that these correlations still exist at fixed σ_e, where galaxies with larger γ_rms are found to be older and more metal-rich. It means that mass density gradients contain information of the stellar population which is not fully accounted for by σ_e. This result puts an extra constraint on our understanding of galaxy quenching. We compare our results with galaxies in the IllustrisTNG hydrodynamical simulations and find that, at fixed σ_e, similar trends exist with age, the bulge fraction, and the total mass density slope but, unlike observations, no correlation with metallicity can be detected in the simulations.