Spatially resolved stellar-to-total dynamical mass relation

Radial variations, gradients, and profiles of galaxy stellar populations

¹ INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5 50125, Firenze (FI), Italy
² Physics and Astronomy Department of the University of Florence, Via G. Sansone 50019, Sesto Fiorentino (FI), Italy
³ Physics Department of the University of Trento, Via Sommarive 14 38123, Povo (TN), Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 August 2025
Accepted: 18 January 2026

Abstract

Context. In our standard cosmological model, galaxy assembly is inherently linked to the hierarchical growth of dark matter halos, which provide the gravitational framework in which highly complex baryonic processes unfold. Although galaxy evolution is governed by the interplay between baryonic physics and halo assembly, the extent to which halo properties shape observed galaxy properties remains unclear. With current observational challenges in measuring halo properties, the stellar-to-total dynamical mass relation is introduced as an alternative observationally based plane that is sensitive to the dark matter content within galaxies.

Aims. We aim to investigate how spatially resolved stellar population properties vary across the stellar-to-total dynamical mass relation.

Methods. We analyzed optical integral-field spectrocopic data from the Calar Alto Legacy Integral Field Area Survey (CALIFA) coupled with photometry for a sample of 265 galaxies to derive their spatially resolved ages and metallicities through a Bayesian fitting framework fed with an extensive library of model spectra based on stochastic star formation and metallicity histories and dust attenuation. We studied these properties in terms of both stellar and total dynamical mass, derived in a completely independent manner. Total masses correspond to enclosed masses within an aperture of three effective radii obtained through detailed Jeans dynamical modeling of the galaxies’ stellar kinematics.

Results. We find that galaxy ages and metallicities measured at different radial annuli depend both on stellar and total mass, typically showing an anti-correlation with total mass after accounting for the strong correlation with stellar mass. Yet, age and [M/H] show a distinct behavior in relation to galactocentric distance. While the dependence of age on total mass becomes more prominent in the outskirts, the one of [M/H] is significant in the inner regions. This behavior is reflected in the galaxies’ stellar population profiles, which appear to be connected to the galaxies’ morphological type. In particular, intermediate-mass (M_★ ∼ 10^10.5−11 M_⊙) early types have higher stellar-to-total mass ratios and flatter age profiles with overall old ages, and steep negative [M/H] profiles, whereas later types have lower stellar-to-total mass ratios, negative age profiles with younger ages and less steep negative [M/H] profiles. Consistently, the scatter of the stellar-total-dynamical mass relation is connected to differences in the stellar population gradients, although more strongly for age. Specifically, galaxies have flatter age gradients and steeper negative [M/H] ones with increasing stellar mass at fixed total mass. Conversely, galaxies of a given stellar mass exhibit age gradients that become more negative with increasing total mass, while the metallicity gradients become less steep.

Conclusions. Our findings reveal that, at fixed stellar mass, total dynamical mass is linked to systematic variations in the stellar populations and their radial gradients, suggesting a relevant role of dark matter halos in shaping galaxy properties. These trends can be interpreted as the imprint of different halo assembly histories across the stellar-to-total dynamical mass relation, where halos that formed earlier host more evolved systems.