The change of the total mass density slope, γ, of early-type galaxies through cosmic time is a probe of evolutionary pathways. Hydrodynamical cosmological simulations show that at high redshifts density profiles of early-type galaxies were on average steep (γ ∼ −3). As redshift approaches zero, gas-poor mergers progressively cause the total mass density slope to approach the ‘isothermal’ slope of γ ∼ −2. Simulations therefore predict steep density slopes at high redshifts, with little to no evolution in density slopes below z ∼ 1. Gravitational lensing results in the same redshift range find the opposite, namely a significant trend of shallow density slopes at high redshifts, becoming steeper as redshift approaches zero. Gravitational lensing results indicate a different evolutionary mechanism for early-type galaxies than dry merging, such as continued gas accretion or off-axis mergers. At redshift zero, isothermal solutions are obtained by both simulations and dynamical modelling. This work applies the Jeans dynamical modelling technique to observations of galaxies at intermediate redshifts (0.29 < z < 0.55) in order to derive density slopes to address the tension between observations and simulations. We combine two-dimensional kinematic fields from Multi Unit Spectroscopic Explorer data with Hubble Space Telescope photometry. The density slopes of 90 early-type galaxies from the Frontier Fields project are presented. The total sample has a median of γ = −2.11 ± 0.03 (standard error), in agreement with dynamical modelling studies at redshift zero. The lack of evolution in total density slopes in the past 4–6 Gyr supports a dry merging model for early-type galaxy evolution.

中文翻译：

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在红移 0.29 < z < 0.55 时使用 Jeans 动力学建模的早期型星系的总质量密度斜率

早期型星系的总质量密度斜率 γ 随宇宙时间的变化是对演化路径的探索。流体动力学宇宙学模拟表明，在高红移时，早期型星系的密度分布平均是陡峭的（γ ∼ -3）。随着红移接近零，贫气合并逐渐导致总质量密度斜率接近 γ ∼ -2 的“等温”斜率。因此，模拟预测了高红移处的陡峭密度斜率，z ∼ 1 以下的密度斜率几乎没有变化。在相同红移范围内的引力透镜结果发现相反，即在高红移处浅密度斜率的显着趋势，变得更陡红移接近零。引力透镜结果表明，早期型星系的演化机制与干合并不同，例如持续的气体吸积或离轴合并。在红移为零时，通过模拟和动态建模获得等温解。这项工作将 Jeans 动力学建模技术应用于中间红移 (0.29 < z < 0.55) 的星系观测，以便推导出密度斜率，以解决观测和模拟之间的紧张关系。我们将来自多单元光谱探测器数据的二维运动场与哈勃太空望远镜测光相结合。展示了来自 Frontier Fields 项目的 90 个早型星系的密度斜率。总样本的中位数为 γ = -2.11 ± 0.03（标准误差），与红移零时的动力学建模研究一致。