SDSS-IV MaNGA: Stellar population correlates with stellar root-mean-square velocity $V_{\mathrm{rms}}$ gradients or total-density-profile slopes at fixed effective velocity dispersion ${\sigma }_{\mathrm{e}}$

Abstract

Galaxy properties are known to correlate most tightly with the galaxy effective stellar velocity dispersion ${\sigma }_{\mathrm{e}}$. Here we look for {\em additional} trends at fixed ${\sigma }_{\mathrm{e}}$ using 1339 galaxies ($M_{\ast }\gtrsim 6\times 10^9$ M${}_{\odot }$) with different morphologies in the MaNGA (DR14) sample with integral-field spectroscopy data. We focus on the gradients (${\gamma }_{\mathrm{rms}}\equiv \sigma (R_{\mathrm{e}}/4)/{\sigma }_{\mathrm{e}}$) of the stellar root-mean-square velocity ($V_{\mathrm{rms}}\equiv \sqrt{V^2+{\sigma }^2}$), which we show traces the total mass density gradient ${\gamma }_{\mathrm{tot}}$ derived from dynamical models and, more weakly, the bulge fraction. We confirm that ${\gamma }_{\mathrm{rms}}$ increases with ${\sigma }_{\mathrm{e}}$, age and metallicity. We additionally find that these correlations still exist at fixed ${\sigma }_{\mathrm{e}}$, where galaxies with larger ${\gamma }_{\mathrm{rms}}$ 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 ${\sigma }_{\mathrm{e}}$. 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 ${\sigma }_{\mathrm{e}}$, 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.

8 pages, 6 figures; Accepted for publication in MNRAS