MaNGA DynPop -- VI. Matter density slopes from dynamical models of 6000 galaxies versus cosmological simulations: the interplay between baryonic and dark matter

TL;DR

This study uses dynamical models of nearly 6000 galaxies from the MaNGA survey to analyze matter density slopes, revealing how stellar and dark matter distributions relate and comparing observations with cosmological simulations.

Contribution

It provides detailed measurements of stellar, dark matter, and total density slopes across galaxy types, and evaluates the accuracy of simulations in reproducing observed galaxy mass distributions.

Findings

Total density slopes approach 2.2 in high-σ galaxies

Stellar and total slopes are tightly correlated

Simulations overestimate dark matter fractions in central regions

Abstract

We try to understand the trends in the mass density slopes as a function of galaxy properties. We use the results from the best Jeans Anisotropic Modelling (JAM) of the integral-field stellar kinematics for near 6000 galaxies from the MaNGA DynPop project, with stellar masses of $10^{9-12}\ {\rm M_{\odot}}$, including both early-type and late-type galaxies. We use the mass-weighted density slopes for the stellar $\overline{\gamma}_*$, dark $\overline{\gamma}_{\rm DM}$, and total $\overline{\gamma}_{\rm T}$ mass from the MaNGA DynPop project. The $\overline{\gamma}_{\rm T}$ approaches a constant value of 2.2 for high $\sigma_{\rm e}$ galaxies, and flattens for lg$(\sigma_{\rm e}/{\rm km\ s^{-1}})\lesssim2.3$, reaching 1.5 for lg$(\sigma_{\rm e}/{\rm km\ s^{-1}})\approx1.8$. The total and stellar slopes track each other tightly, with $\overline{\gamma}_{\rm T}\approx\overline{\gamma}_*-0.174$ over the full $\sigma_{\rm e}$ range. This confirms the dominance of stellar matter within $R_{\rm e}$. We also show that there is no perfect conspiracy between baryonic and dark matter, as $\overline{\gamma}_*$ and $\overline{\gamma}_{\rm DM}$ do not vary inversely within the $\sigma_{\rm e}$ range. We find that the central galaxies from TNG50 and TNG100 simulations do not reproduce the observed galaxy mass distribution, which we attribute to the overestimated dark matter fraction, possibly due to a constant IMF and excessive adiabatic contraction effects in the simulations. Finally, we present the stacked dark matter density profiles and show that they are slightly steeper than the pure dark matter simulation prediction of $\overline{\gamma}_{\rm DM}\approx1$, suggesting moderate adiabatic contraction in the central region of galaxies. Our work demonstrate the power of stellar dynamics modelling for probing the interaction between stellar and dark matter and testing galaxy formation theories.