重子对小尺度下宇宙质量分布的方差和偏度的影响
The effect of baryons on the variance and the skewness of the mass distribution in the universe at small scales
摘要：
我们利用一个体积为（50 Mpc/h）^3的宇宙的宇宙学模拟，研究了重子物理对小尺度宇宙统计的耗散效应。MareNostrum模拟使用AMR代码RAMSES进行，包括当前星系形成理论的大部分物理成分，如金属依赖冷却和紫外线加热，ISM的次网格建模，恒星形成和超新星反馈。我们对只有暗物质的宇宙重新运行了相同的初始条件，作为无重子宇宙统计的参考点。本文介绍了重子物理引起的σ ^2和S_3的小尺度放大的测量结果以及在晕模型框架下对它们的解释。最近的研究表明，在k <~ 10 h/Mpc尺度下，通过修正晕浓度参数，重子对物质功率谱的影响可以得到解释。我们建议扩展这一结果，通过使用晕配置文件，这是一个线性组合的NFW配置文件的暗物质和指数盘配置文件模仿重子组件的中心晕。这种晕的轮廓形式是物理上的，取决于两个参数：盘中重子的质量分数f_d和盘的特征尺度与晕的维里半径之比λ_d。我们发现，对于具有物理意义的参数f_d和lambda_d值，这种复合分布再现了模拟中测量到的小尺度方差和偏度提升，最高可达k ~ 10^2 h/Mpc。虽然像这里提出的模拟通常遭受各种问题相比，观测，我们修改后的晕模型可以作为一个拟合模型，以改善弱透镜收敛谱和偏度测量的宇宙学参数的测定。
英文摘要：
We study the dissipative effects of baryon physics on cosmic statistics at small scales using a cosmological simulation of a (50 Mpc/h)^3 volume of the universe. The MareNostrum simulation was performed using the AMR code RAMSES, and includes most of the physical ingredients which are part of the current theory of galaxy formation, such as metal-dependent cooling and UV heating, subgrid modelling of the ISM, star formation and supernova feedback. We re-ran the same initial conditions for a dark matter only universe, as a reference point for baryon-free cosmic statistics. In this paper, we present the measured small-scale amplification of sigma^2 and S_3 due to baryonic physics and their interpretation in the framework of the halo model. As shown in recent studies, the effect of baryons on the matter power spectrum can be accounted for at scales k <~ 10 h/Mpc by modifying the halo concentration parameter. We propose to extend this result by using a halo profile which is a linear combination of a NFW profile for the dark matter and an exponential disk profile mimicking the baryonic component at the heart of the halo. This halo profile form is physically motivated, and depends on two parameters, the mass fraction f_d of baryons in the disk, and the ratio lambda_d of the disk's characteristic scale to the halo's virial radius. We find this composite profile to reproduce both the small-scale variance and skewness boosts measured in the simulation up to k ~ 10^2 h/Mpc for physically meaningful values of the parameters f_d and lambda_d. Although simulations like the one presented here usually suffer from various problems when compared to observations, our modified halo model could be used as a fitting model to improve the determination of cosmological parameters from weak lensing convergence spectra and skewness measurements.
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