大质量早型星系的结构与动力学：关于一个有效半径内的同调、等温和各向同性
The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
摘要：
基于58个SLACS强透镜早型星系的直接总质量和恒星速度色散测量，我们发现，在一个有效半径内，M_eff >= 3 × 10^10 M_sun的大质量椭圆星系可以很好地近似为一个幂律椭球，其平均对数密度斜率<gamma '_LD> = -dlog（rho_tot）/dlog（r）=2.085^{+0.025}_{-0.018}（平均随机误差），β_r=0，± 0.1（系统）和σ_γ ' <= 0.20^{+0.04}_{-0.02}固有散射（所有误差指示68% CL）。尽管星系间的密度-斜率存在内在差异，但我们发现γ '_LD与星系质量（M_eff）、重标半径（R_einst/R_eff）或红移无关。基于比例关系，平均对数密度斜率可以以完全独立于动力学的替代方式导出，得到<γ '_SR>=1.959 +-0.077。两个值之间的协议达到<beta_r>=0.45 +- 0.25，符合轻度径向各向异性。这种一致性支持了我们结果的稳健性，尽管质光比随星系总质量的增加而增加：M_eff ~ L_{V,eff} ^（1.363+-0.056）。我们的结论是，大质量早型星系的结构接近同源的接近等温的总密度分布（<= 10%的内禀散射），最多有一些温和的径向各向异性。我们的研究结果提供了新的观测限制星系形成和演化的情况下，覆盖四个陀螺回看时间。
英文摘要：
Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and stellar-velocity dispersion measurements, we find that inside one effective radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are well-approximated by a power-law ellipsoid with an average logaritmic density slope of <gamma'_LD> = -dlog(rho_tot)/dlog(r)=2.085^{+0.025}_{-0.018} (random error on mean) for isotropic orbits with beta_r=0, +-0.1 (syst.) and sigma_gamma' <= 0.20^{+0.04}_{-0.02} intrinsic scatter (all errors indicate the 68 percent CL). We find no correlation of gamma'_LD with galaxy mass (M_eff), rescaled radius (i.e. R_einst/R_eff) or redshift, despite intrinsic differences in density-slope between galaxies. Based on scaling relations, the average logarithmic density slope can be derived in an alternative manner, fully independent from dynamics, yielding <gamma'_SR>=1.959 +- 0.077. Agreement between the two values is reached for <beta_r> =0.45 +- 0.25, consistent with mild radial anisotropy. This agreement supports the robustness of our results, despite the increase in mass-to-light ratio with total galaxy mass: M_eff ~ L_{V,eff}^(1.363+-0.056). We conclude that massive early-type galaxies are structurally close-to homologous with close-to isothermal total density profiles (<=10 percent intrinsic scatter) and have at most some mild radial anisotropy. Our results provide new observational limits on galaxy formation and evolution scenarios, covering four Gyr look-back time.
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