MAGNUS III: Mild evolution of the total density slope in massive early-type galaxies since z$\sim$1 from dynamical modeling of MUSE integral-field stellar kinematics

TL;DR

This study analyzes the evolution of the total mass density slope in massive early-type galaxies over the last 6.5 billion years, finding a mild steepening trend consistent with dissipative assembly processes.

Contribution

It provides a homogeneous dynamical analysis of ~200 intermediate-redshift ETGs combined with local data, revealing a statistically significant evolution of the density slope.

Findings

Total density slope is approximately isothermal at intermediate redshift.

The median slope evolves from 2.19 at z~0.44 to 2.26 at z~0.04.

The slope evolution is robust and suggests dissipative processes in galaxy assembly.

Abstract

We investigate the total mass density slope evolution in massive early-type galaxies (ETGs) over the last 6.5 billion years ($0 < z < 0.75$). We perform a detailed dynamical analysis of approximately 200 ETGs spanning the redshift range $0.24 < z < 0.75$, utilizing spatially resolved stellar kinematics derived from high signal-to-noise ratio (S/N) MUSE-DEEP spectroscopy and surface brightness models from high-resolution HST imaging. We constrain mass distributions using the Jeans Anisotropic Modeling (JAM) technique coupled with Multi-Gaussian Expansion (MGE) method. To rigorously constrain evolutionary trends, we combine this intermediate-redshift dataset with a local ETG sample ($z \sim 0.05$) from the MaNGA survey. We adopt dynamical constraints for the local sample derived using an identical homogeneous methodology, ensuring a strictly consistent comparison. We found that the total density profiles of the intermediate-redshift ETG sample are approximately isothermal and exhibit a median mass-weighted total density slope, $<\gamma_{\rm T}>=2.19 \pm 0.01$ at $<z>=0.44$, which is shallower than the local baseline of $<\gamma_{\rm T}> = 2.26 \pm 0.01$ at $<z>=0.04$. This structural shift corresponds to a redshift gradient of $\mathrm{d} \gamma_{\rm T}/\mathrm{d} z \approx -0.20 \pm 0.03$, detected at $\sim$5-$\sigma$ significance. We demonstrate that this trend is robust against model assumptions and persists even when restricting the analysis to high-velocity dispersion systems ($\sigma_e > 150$ km/s). Our findings are consistent with previous lensing-based studies and in tension with cosmological simulations. The observed steepening suggests that dissipative processes, such as gas-rich accretion and mergers, must play a non-negligible role in the late-stage assembly of massive ETGs.