标题： 冷热暗物质和CDM宇宙中的星系团：与CfA的比较 显示英文标题

标题： Galaxy Groups in Cold + Hot and CDM Universes: Comparison with CfA

摘要： 这封信提出了新的高分辨率$\Omega=1$冷+热暗物质（CHDM）和冷暗物质（CDM）模拟的结果。这些模拟中集团的特性反映了与CDM相比，CHDM在小尺度上具有较低的小尺度速度以及在大小尺度上形成明显丝状结构的更大倾向。发现集团中星系的比例和中位数集团均方根速度是区分模型的强大判据。我们将这两个特征结合成一个非常稳健的统计量，即中位数集团均方根速度$v_{\rm gr}(f_{\rm gr})$作为集团中星系比例$f_{\rm gr}$的函数。使用这个统计量，我们以一种仔细且一致的方式将“观测”模拟与CfA数据在红移空间进行比较。我们发现CHDM仍然是一个有前景的模型，例如$v_{\rmgr}(0.45) \approx 125 \pm 25 \kms$与CfA数据一致，而b=1.0（与COBE相容）或b=1.5的CDM，两者都给出$v_{\rm gr}(0.45) \approx 400 \pm 25 \kms$，几乎可以被排除。 使用中位数$M/L$，观察到的$\Omega$值为$0.10$（CHDM）至$0.38$（CDM）。 显示英文摘要

摘要： This letter presents results of new high resolution $\Omega=1$ Cold + Hot Dark Matter (CHDM) and Cold Dark Matter (CDM) simulations. Properties of groups in these simulations reflect the lower small-scale velocities and the greater tendency to form distinct filaments on both small and large scales in CHDM as compared to CDM. The fraction of galaxies in groups and the median group rms velocity are found to be powerful discriminators between models. We combine these two features into a very robust statistic, median group rms velocity $v_{\rm gr}(f_{\rm gr})$ as a function of the fraction $f_{\rm gr}$ of galaxies in groups. Using this statistic, we compare ``observed'' simulations to CfA data in redshift space in a careful and consistent way. We find that CHDM remains a promising model, with for example $v_{\rmgr}(0.45) \approx 125 \pm 25 \kms$ in agreement with the CfA data, while CDM with bias b=1.0 (COBE-compatible) or b=1.5, both giving $v_{\rm gr}(0.45) \approx 400 \pm 25 \kms$, can be virtually ruled out. Using median $M/L$, the observed value of $\Omega$ is $0.10$ (CHDM) to $0.38$ (CDM).