标题： 早期型星系内部有多少暗物质？ 显示英文标题

标题： How much dark matter is there inside early-type galaxies?

摘要： 我们研究早型星系（ETGs）有效半径（r_e）内的发光质量与动力学质量之间的关系，以寻找这两种质量之间的差异。 我们假设牛顿动力学，并认为这两种质量之间的任何差异都是由于暗物质的存在。 我们使用来自斯隆数字巡天第九数据发布中的几个早型星系样本——从19 000到98 000个天体不等——进行研究。 我们对星系样本进行了蒙特卡洛（MC）模拟，并将其与真实样本进行比较。 主要结果是：i) MC模拟显示，动力学质量与发光质量的分布取决于早型星系所处的质量范围（几何效应）。 这种依赖性是由选择效应和早型星系的固有特性引起的。 ii) 在r_e内暗物质的量约为7% ± 22%。 iii) 这一暗物质的量低于文献中找到的最小估计值（10%），并且比文献估计值的平均值（30%）低四倍。 然而，如果我们考虑相关的误差，我们的估计值与文献平均值在同一数量级。 显示英文摘要

摘要： We study the luminous mass as a function of the dynamical mass inside the effective radius (r_e) of early-type galaxies (ETGs) to search for differences between these masses. We assume Newtonian dynamics and that any difference between these masses is due to the presence of dark matter. We use several samples of ETGs -ranging from 19 000 to 98 000 objects- from the ninth data release of the Sloan Digital Sky Survey. We perform Monte Carlo (MC) simulations of galaxy samples and compare them with real samples. The main results are: i) MC simulations show that the distribution of the dynamical vs. luminous mass depends on the mass range where the ETGs are distributed (geometric effect). This dependence is caused by selection effects and intrinsic properties of the ETGs. ii) The amount of dark matter inside r_e is approximately 7% +- 22%. iii) This amount of dark matter is lower than the minimum estimate (10%) found in the literature and four times lower than the average (30%) of literature estimates. However, if we consider the associated error, our estimate is of the order of the literature average.