[论文解读] LCDM Correctly Predicts Basic Statistics of Galaxies: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, and Velocity Function

Sebastian Trujillo-Gomez, Anatoly Klypin+2 more|arXiv (Cornell University)|May 7, 2010

Galaxies: Formation, Evolution, Phenomena被引用 4

一句话总结

本文表明，标准ΛCDM宇宙学模型通过使用高分辨率的Bolshoi暗物质模拟和丰度匹配法，成功预测了关键星系统计量——光度-速度关系、重子质量-速度关系以及速度函数。对于圆周速度大于50 km s⁻¹的星系，其预测与观测结果吻合良好，但在该阈值以下仍存在差异。

ABSTRACT

It has long been regarded as difficult if not impossible for a cosmological model to account simultaneously for the galaxy luminosity, mass, and velocity distributions. We revisit this issue using a modern compilation of observational data along with the most advanced large-scale cosmological simulation of dark matter. We find that the standard cosmological model fits – at least on average – all basic statistics of galaxies with circular velocities Vcirc > 50 km s −1 calculated at ∼10 kpc radius. Besides an SDSS-based r-band luminosity function, our primary observational constraint is the luminosity-velocity relation – which generalizes the Tully-Fisher and Faber-Jackson relations in allowing all types of galaxies to be included, and provides a fundamental benchmark to be reproduced by any theory of galaxy formation. We have compiled data for a variety of galaxies ranging from dwarf irregulars to giant ellipticals. The data present a clear monotonic luminosity-velocity relation from ∼ 50 km s to ∼ 500 km s, with a bend below ∼ 80 km s and a systematic offset between lateand early-type galaxies. For comparison to theory, we make use of our new ΛCDM “Bolshoi” simulation of dark matter, which has unprecedented mass and force resolution over a large cosmological volume, while using an up-todate set of initial conditions. We use an abundance-matching technique to assign rank-ordered galaxy luminosities to the dark matter halos, a procedure which automatically fits the empirical luminosity function and provides a predicted luminosity-velocity relation that can be checked against observations. The adiabatic contraction of dark matter halos in response to the infall of the baryons is included as an optional model ingredient. The resulting predictions for the luminosity-velocity relation are in good agreement with the available data on both early-type and late-type galaxies for the magnitude range from Mr = −14 to Mr = −22. We also compare our predictions for the cold baryon mass of galaxies as a function of circular velocity with the available observations, again finding good agreement except perhaps at the highest Vcirc. Finally, the predicted circular velocity function is in agreement with the galaxy velocity function from 80 to 400 km s, using the HIPASS survey for late-type and SDSS for early-type galaxies. However, in agreement with other recent results, we find that the dark matter halos with Vcirc < 50 km s are much more abundant than observed galaxies with the same Vcirc. Subject headings: cosmology: theory — dark matter — galaxies: halos — galaxies: structure

研究动机与目标

• 检验ΛCDM模型是否能够同时再现诸如光度、质量与速度分布等基本星系统计量。
• 解决长期存在的挑战：即在不同形态的星系中，将宇宙学模型与观测到的星属性相协调。
• 利用现代高分辨率暗物质模拟和最新观测数据，评估ΛCDM框架的表现。
• 探究在低圆周速度下，预测与观测到的星系丰度差异的根源。
• 评估绝热压缩在改善光度-速度关系预测中的作用。

提出的方法

• 利用Bolshoi ΛCDM暗物质模拟，其在大宇宙体积内具有前所未有的质量与力分辨率。
• 应用丰度匹配法，根据排序后的晕属性将星系光度分配给暗物质晕，以确保与观测到的光度函数一致。
• 将暗物质晕在重子物质下落作用下的绝热压缩作为物理解释调整，以改进预测结果。
• 将预测的光度-速度关系与从矮不规则星系到巨型椭圆星系的观测数据进行比较。
• 构建预测的圆周速度函数，并与HIPASS和SDSS巡天的实测数据进行对比。
• 在同一个宇宙学模型内，使用一致的框架评估多种星系统计量的预测表现。

实验结果

研究问题

• RQ1 ΛCDM模型能否同时再现所有星系类型中观测到的光度-速度关系？
• RQ2 该模型在高和低圆周速度下对重子质量-速度关系的预测效果如何？
• RQ3 引入绝热压缩后，预测与观测的一致性改善程度如何？
• RQ4 为何低圆周速度暗物质晕的丰度远高于观测到的星系？
• RQ5 预测的速度函数是否与HIPASS和SDSS等大型巡天的实测结果一致？

主要发现

• 利用Bolshoi模拟和丰度匹配法，ΛCDM模型成功预测了圆周速度在约50至约500 km s⁻¹范围内的星系光度-速度关系。
• 该模型预测的光度-速度关系在Mr = −14至Mr = −22的星等范围内，对早型星系和晚型星系均与观测结果高度一致。
• 模型预测的重子质量-速度关系与观测结果基本吻合，但在最高圆周速度处可能略有偏差。
• 预测的圆周速度函数在80至400 km s⁻¹范围内与HIPASS和SDSS的实测数据高度一致。
• 在Vcirc ≈ 50 km s⁻¹以下，仍存在显著差异，即暗物质晕的丰度远高于观测到的星系。
• 引入绝热压缩可进一步提升模型与光度-速度关系的一致性，尽管即使不引入该机制，整体预测已具较强一致性。