Evolution of total density slopes of cluster galaxies using integral field spectroscopy

The change of the total mass density slope, γ, of early-type galaxies through cosmic time is a probe of evolutionary pathways. A trend towards steeper slopes with greater lookback time indicates the predominance of gas-poor mergers, whilst more shallow slopes with greater lookback times point to gas-rich mergers. Gravitational lensing observations at redshifts up to z ∼ 1 lend strength to a gas-rich merger scenario, which is in tension with hydrodynamical cosmological simulation predictions of gas-poor minor mergers being fundamental to galaxy mass growth after z ∼ 2. At redshift zero, isothermal solutions are obtained by both simulations and dynamical modelling. This work extends the dynamical modelling technique to intermediate redshifts (0.3 < z < 0.55) in order to derive density slopes, combining two-dimensional kinematic fields from MUSE data with photometry from the Hubble Space Telescope. The density slopes of 50 galaxies from the Frontier Fields project, majority early-type, are presented. A linear evolution in the slope of dγ/dz = −0.34 ± 0.18 is found, supporting a picture of galaxy growth via gas-poor minor mergers.