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

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, $<{\gamma }_{\mathrm{T}}>=2.19\pm 0.01$ at $<z>=0.44$, which is shallower than the local baseline of $<{\gamma }_{\mathrm{T}}>=2.26\pm 0.01$ at $<z>=0.04$. This structural shift corresponds to a redshift gradient of $\mathrm{d}{\gamma }_{\mathrm{T}}/\mathrm{d}z\approx -0.20\pm 0.03$, 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.

submitted to ApJ