早型星系类Salpeter初始质量函数在氢燃烧极限附近的低质量截止
A low-mass cut-off near the hydrogen burning limit for Salpeter-like initial mass functions in early-type galaxies
摘要：
我们对两个速度色散分别为245 km/s和325 km/s的大质量早型透镜星系的恒星初始质量函数（IMF）的性质进行了详细的研究。我们比较从两个完全独立的方法得到的推论：（一）结合引力透镜和恒星动力学（L&D）分析的数据集采用自洽轴对称模型，和（ii）光谱简单的恒星星族（SSP）分析的光学线强度指数，假设单一的幂律IMF。从这两种方法的结果被发现是一致的1-西格玛的不确定性。这两个星系都符合萨尔彼得IMF（x = 2.35的幂律斜率），这是强烈倾向于夏布里耶IMF（x = 1.8），从联合分析推断的概率分别为89%和99%。对于两个星系来说，明显比萨尔皮特（x >= 3.0）陡峭的底部重IMF被排除在决定性的证据之外（贝叶斯因子B > 1000），因为它们超过了从L&D约束得出的总质量。我们的分析允许，第一次，推断低质量的国际货币基金组织（M_低）的截止。结合两个星系的联合L&D和SSP分析，我们推断IMF斜率x = 2.22 +/- 0.14，与Salpeter IMF一致，低质量极限M_low = 0.13 +/- 0.03 M_sun，略高于氢燃烧极限。
英文摘要：
We conduct a detailed investigation of the properties of the stellar initial mass function (IMF) in two massive early-type lens galaxies with velocity dispersions of sigma ~245 km/s and sigma ~325 km/s, for which both HST imaging and X-Shooter spectra are available. We compare the inferences obtained from two fully independent methods: (i) a combined gravitational lensing and stellar dynamics (L&D) analysis of the data sets employing self-consistent axisymmetric models, and (ii) a spectroscopic simple stellar population (SSP) analysis of optical line-strength indices, assuming single power-law IMFs. The results from the two approaches are found to be in agreement within the 1-sigma uncertainties. Both galaxies are consistent with having a Salpeter IMF (power-law slope of x = 2.35), which is strongly favoured over a Chabrier IMF (x = 1.8), with probabilities inferred from the joint analysis of 89% and 99%, respectively. Bottom-heavy IMFs significantly steeper than Salpeter (x >= 3.0) are ruled out with decisive evidence (Bayes factor B > 1000) for both galaxies, as they exceed the total mass derived from the L&D constraints. Our analysis allows, for the first time, the inference of the low-mass cut-off of the IMF (M_low). Combining the joint L&D and SSP analyses of both galaxies, we infer an IMF slope of x = 2.22 +/- 0.14, consistent with Salpeter IMF, and a low-mass limit M_low = 0.13 +/- 0.03 M_sun, just above the hydrogen burning limit.
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