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arXiv 1801.01883astro-ph.GAastro-ph.CO
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来自弱和强透镜的大质量星系的恒星质光比径向变化的证据

Evidence for radial variations in the stellar mass-to-light ratio of massive galaxies from weak and strong lensing

Alessandro Sonnenfeld, Alexie Leauthaud, Matthew W. Auger, Raphael Gavazzi, Tommaso Treu, Surhud More, Yutaka Komiyama

摘要:

结合恒星动力学和强引力透镜,可以对大质量星系的初始质量函数(IMF)进行约束。然而,这种方法受到暗物质密度分布和恒星质光比之间简并的限制。在这项工作中,我们减少这种简并结合弱透镜与强透镜和恒星运动学。我们的分析基于两个星系样本:SLACS调查的45个强透镜和SDSS主要光谱样本中的1,700个大质量静止星系,以及Hyper Suprime-Cam调查的弱透镜测量。我们使用贝叶斯分层方法来联合建模所有三个观测。我们拟合的数据与模型的复杂性不同,并表明,一个模型与径向梯度的恒星质量与光的比例,需要同时描述两个星系样本。这个结果是由具有非常陡峭的总密度分布的强透镜的子集驱动的,其不能由没有梯度的模型拟合。我们的测量无法确定是否$M_*/L$梯度是由于固定IMF的恒星星族参数的变化,或在IMF本身的梯度。包含$M_*/L$梯度显着降低推断IMF归一化,与以前的基于透镜的研究相比,与确切的值取决于假设的暗物质配置文件。强透镜选择的主要作用是使恒星质量分布向高质量端移动,而在恒星质量不变的情况下,对晕质量和恒星IMF分布的影响不明显。

英文摘要:

The Initial Mass Function (IMF) for massive galaxies can be constrained by combining stellar dynamics with strong gravitational lensing. However, this method is limited by degeneracies between the density profile of dark matter and the stellar mass-to-light ratio. In this work we reduce this degeneracy by combining weak lensing together with strong lensing and stellar kinematics. Our analysis is based on two galaxy samples: 45 strong lenses from the SLACS survey and 1,700 massive quiescent galaxies from the SDSS main spectroscopic sample with weak lensing measurements from the Hyper Suprime-Cam survey. We use a Bayesian hierarchical approach to jointly model all three observables. We fit the data with models of varying complexity and show that a model with a radial gradient in the stellar mass-to-light ratio is required to simultaneously describe both galaxy samples. This result is driven by a subset of strong lenses with very steep total density profile, that cannot be fitted by models with no gradient. Our measurements are unable to determine whether $M_*/L$ gradients are due to variations in stellar population parameters at fixed IMF, or to gradients in the IMF itself. The inclusion of $M_*/L$ gradients decreases dramatically the inferred IMF normalisation, compared to previous lensing-based studies, with the exact value depending on the assumed dark matter profile. The main effect of strong lensing selection is to shift the stellar mass distribution towards the high mass end, while the halo mass and stellar IMF distribution at fixed stellar mass are not significantly affected.

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