该领域是否存在“太大而不能倒”的问题？
Is there a "too big to fail" problem in the field?
摘要：
我们使用阿雷西博遗产快速ALFA（ALCAFA）21厘米调查测量星系的数量密度作为其旋转速度的函数，$V_\mathrm{rot,HI}$（从其21厘米发射线的宽度推断）。基于测量的速度函数，我们统计连接星系与它们的宿主晕，通过丰度匹配。在λ冷暗物质（$Λ$ CDM）宇宙学中，矮星系被认为是由比测量的星系速度更大的质量的晕所承载的;如果允许更小的晕承载星系，那么ALMARFA将测量到更高的星系数密度。然后，我们通过分析富含气体的矮星系的文献样本的运动学，寻求观测验证这一预测的趋势。我们发现，星系与$V_\mathrm{rot,HI} \lesssim 25$ $\mathrm{km} \, \mathrm{s}^{-1}$是运动学不兼容的预测$Λ$ CDM主机晕，在这个意义上，主机太大，无法容纳在测量的星系旋转曲线。这个问题类似于银河系明亮的卫星所面临的“太大而不能倒”的问题，但这里它涉及的是该领域的极端矮星系。因此，基于具体卫星进程的解决办法不适用于这种情况。我们的结果证实了之前基于光学测量数据的研究结果，并解决了这些工作中存在的许多观测系统学问题。此外，我们指出了可能强烈影响我们结论的假设和不确定性。我们发现，其中最重要的两个-即重子效应的丰度晕和旋转曲线的晕-似乎没有能力解决报告的差异。
英文摘要：
We use the Arecibo legacy fast ALFA (ALFALFA) 21cm survey to measure the number density of galaxies as a function of their rotational velocity, $V_\mathrm{rot,HI}$ (as inferred from the width of their 21cm emission line). Based on the measured velocity function we statistically connect galaxies with their host halo, via abundance matching. In a lambda cold dark matter ($Λ$CDM) cosmology, dwarf galaxies are expected to be hosted by halos that are significantly more massive than indicated by the measured galactic velocity; if smaller halos were allowed to host galaxies, then ALFALFA would measure a much higher galactic number density. We then seek observational verification of this predicted trend by analyzing the kinematics of a literature sample of gas-rich dwarf galaxies. We find that galaxies with $V_\mathrm{rot,HI} \lesssim 25$ $\mathrm{km} \, \mathrm{s}^{-1}$ are kinematically incompatible with their predicted $Λ$CDM host halos, in the sense that hosts are too massive to be accommodated within the measured galactic rotation curves. This issue is analogous to the "too big to fail" problem faced by the bright satellites of the Milky Way, but here it concerns extreme dwarf galaxies in the field. Consequently, solutions based on satellite-specific processes are not applicable in this context. Our result confirms the findings of previous studies based on optical survey data and addresses a number of observational systematics present in these works. Furthermore, we point out the assumptions and uncertainties that could strongly affect our conclusions. We show that the two most important among them -namely baryonic effects on the abundances of halos and on the rotation curves of halos- do not seem capable of resolving the reported discrepancy.
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