空洞的空虚：LCDM模型的另一个过剩问题
The emptiness of voids: yet another over-abundance problem for the LCDM model
摘要：
本文研究了在距离为4- 8 Mpc范围内，包含MB=-10-12的星系的观测样品的光度函数、特殊速度和局域体积（LV）中的空洞大小。将结果与标准宇宙学LCDM模型的预测进行比较，我们发现该理论面临着一个严重的问题：与观测到的矮星系数量相比，它预测的矮晕数量要多出10倍。在LV中，我们确定了尺寸范围从1到4.5Mpc的空隙，并将空隙尺寸的观测分布与具有WMAP 1和WMAP 3参数的LCDM模型的非常高分辨率的模拟中的空隙进行了比较。只有当σ 8 = 0.9时，我们使用圆速度Vc大于40-45 km/s（Mvir=（1-2）e10 msun）的晕; σ 8 = 0.75时，我们使用Vc> 35 km/s（Mvir=（6-8）e9 msun）的晕时，理论空函数才能与观测值非常好地匹配。我们排除了LCDM模型中圆速度<35 km/s的晕可以容纳MB=-12的星系的可能性：LCDM模型中有太多的小晕，导致与观测相比空洞太小。问题是，许多观测到的矮星系的HI旋转速度低于25 km/s，这与LCDM的预测严格矛盾。因此，LCDM模型面临着同样的过剩问题，这与LG中的卫星数量有关。我们还估计了与哈勃流σ H的均方根偏差，并发现在我们的大多数LV模型候选者中，均方根特有速度与观测值σ H = 50 km/s（距离小于3 Mpc）和σ H = 80 km/s（距离小于8 Mpc）一致。在距离4（8）Mpc处，观测到的星系超密度为3.5-5.5（1.3-1.6）--明显大于通常假设的。
英文摘要：
We study the luminosity function, the peculiar velocities, and the sizes of voids in the Local Volume (LV) in observational samples of galaxies which contain galaxies down to MB=-10-12 within the distance 4-8Mpc. Comparing the results with the predictions of the standard cosmological LCDM model, we find that the theory faces a sever problem: it predicts a factor of ten more dwarf haloes as compared with the observed number of dwarf galaxies. In the LV we identify voids with sizes ranging from 1 to 4.5Mpc and compare the observational distribution of void sizes with the voids in very high resolution simulations of the LCDM model with WMAP1 and WMAP3 parameters. The theoretical void function matches the observations remarkably well only if we use haloes with circular velocities Vc larger than 40-45 km/s (Mvir=(1-2)e10msun) for models with with sigma8 = 0.9 and Vc>35km/s (Mvir=(6-8)e9msun) for sigma8 = 0.75. We exclude the possibility that in the LCDM model haloes with circular velocities < 35km/s can host galaxies as bright as MB=-12: there are too many small haloes in the LCDM model resulting in voids being too small as compared with the observations. The problem is that many of the observed dwarf galaxies have HI rotational velocities below 25km/s that strictly contradicts the LCDM predictions. Thus, the LCDM model faces the same overabundance problem, which it had with the number of satellites in the LG. We also estimate the rms deviations from the Hubble flow sigmaH and find that in most of our model LV-candidates the rms peculiar velocities are consistent with observational values sigmaH=50km/s for distances less than 3Mpc and sigmaH=80km/s for distances less than 8Mpc. At distances 4 (8) Mpc, the observed overdensities of galaxies are 3.5-5.5 (1.3-1.6) -- significantly larger than typically assumed.
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