MaNGA DynPop -- V. The dark-matter fraction versus stellar velocity dispersion relation and stellar initial mass function variations in galaxies: dynamical models and full spectrum fitting of integral-field spectroscopy

Abstract

Using the final MaNGA sample of 10K galaxies, we investigate the dark matter fraction $f_{\mathrm{DM}}$ within one half-light radius $R_{\mathrm{e}}$ for about 6K galaxies with good kinematics spanning a wide range of morphologies and stellar velocity dispersion. We employ two techniques to estimate $f_{\mathrm{DM}}$: (i) Jeans Anisotropic Modelling (JAM), which performs dark matter decomposition based on stellar kinematics and (ii) comparing the total dynamical mass-to-light ratios $(M/L{)}_{\mathrm{JAM}}$ and $(M_{\ast }/L{)}_{\mathrm{SPS}}$ from Stellar Population Synthesis (SPS). We find that both methods consistently show a significant trend of increasing $f_{\mathrm{DM}}$ with decreasing ${\sigma }_{\mathrm{e}}$ and low $f_{\mathrm{DM}}$ at larger ${\sigma }_{\mathrm{e}}$. For 235 early-type galaxies with the best models, we explore the variation of stellar initial mass function (IMF) by comparing the stellar mass-to-light ratios from JAM and SPS. We confirm that the stellar mass excess factor ${\alpha }_{\mathrm{IMF}}$ increases with ${\sigma }_{\mathrm{e}}$, consistent with previous studies that reported a transition from Chabrier-like to Salpeter IMF among galaxies. We show that the ${\alpha }_{\mathrm{IMF}}$ trend cannot be driven by $M_{\ast }/L$ or IMF gradients as it persists when allowing for radial gradients in our model. We find no evidence for the total $M/L$ increasing toward the centre. We detect weak positive correlations between ${\alpha }_{\mathrm{IMF}}$ and age, but no correlations with metallicity. We stack galaxy spectra according to their ${\alpha }_{\mathrm{IMF}}$ to search for differences in IMF-sensitive spectral features (e.g. the $\mathrm{N}{\mathrm{a}}_{\mathrm{I}}$ doublet). We only find marginal evidence for such differences, which casts doubt on the validity of one or both methods to measure the IMF.

20 pages, 12 figures, 2 tables; Accepted for publication in MNRAS on 22 April 2024

Cited by in corpus (3)

• MaNGA DynPop -- III. Stellar dynamics versus stellar population relations in 6000 early-type and spiral galaxies: Fundamental Plane, mass-to-light ratios, total density slopes, and dark matter fractions
• MaNGA DynPop -- IV. Stacked total density profile of galaxy groups and clusters from combining dynamical models of integral-field stellar kinematics and galaxy-galaxy lensing
• MaNGA DynPop -- VI. Matter density slopes from dynamical models of 6000 galaxies versus cosmological simulations: the interplay between baryonic and dark matter