Project Dinos II: Redshift evolution of dark and luminous matter density profiles in strong-lensing elliptical galaxies across $0.1 < z < 0.9$

We present a new measurement of the dark and luminous matter distribution of massive elliptical galaxies, and their evolution with redshift, by combining strong lensing and dynamical observables. Our sample of 56 lens galaxies covers a redshift range of $0.090 \leq z_{\rm l} \leq 0.884$. By combining new Hubble Space Telescope imaging with previously observed velocity dispersion and line-of-sight measurements, we decompose the luminous matter profile from the dark matter profile and perform a Bayesian hierarchical analysis to constrain the population-level properties of both profiles. We find that the inner slope of the dark matter density profile ("cusp"; $\rho_{\rm DM} \propto r^{-\gamma_{\rm in}}$) is consistent ($\mu_{\gamma_{\rm in}}=0.97^{+0.03}_{-0.03}$ with $\leq0.07$ intrinsic scatter) with a standard Navarro-Frenk-White (NFW; $\gamma_{\rm in}=1$) at $z=0.35$. Additionally, we find an appreciable evolution with redshift ($d\log(\gamma_{\rm in})/dz=-0.44^{+0.14}_{-0.15}$) resulting in a shallower slope (of $> 2 \sigma$ tension from NFW) at redshifts $z \ge 0.49$. This is in excellent agreement with previous population-level observational studies, as well as with predictions from hydrodynamical simulations such as IllustrisTNG. We also find the stellar mass-to-light ratio at the population level is consistent with that of a Salpeter initial mass function, a small stellar mass-to-light gradient ($\kappa_{*}(r)\propto r^{-\eta}$, with $\overline{\eta} \leq 5 \times 10^{-5}$), and isotropic stellar orbits. Our averaged total mass density profile is consistent with a power-law profile within 0.25 to 4 Einstein radii ($\overline{\gamma} = 2.24 \pm 0.14$), with an internal mass-sheet transformation parameter $\overline{\lambda} = 0.96 \pm 0.03$ consistent with no mass sheet. Our findings confirm the validity of the standard mass models used for time-delay cosmography.