2 PIGG星系群与2dFGRS星系的成团
Clustering of 2PIGG galaxy groups with 2dFGRS galaxies
摘要：
由于类星体透镜效应的迹象表明星系团的质量可能比预期的要大，我们对2 PIGG星系团和星系团的质量作了新的动力学估算。我们分析了星系团-星系交叉关联函数的红移畸变与星系团成员的关系，并将z<0.12的2 PIGG星系团与完整的2dF星系表进行了交叉关联。我们已经作出了估计的动态下落参数β和新的估计的群速度色散。我们首先发现，全三维红移空间互相关联函数xi_{cg}的振幅随群成员数单调上升.我们使用一个简单的线性理论模型来拟合xi（sigma，pi）在5<s<40 h ^{-1}Mpc的范围内。我们发现，数据的β值与隶属度的关系在中等集团成员数n~20或L~2x10^11h^-2Lsun时显示出最小值，这意味着无论是小集团还是富集团，偏差和M/L比值都显著增加（~5x）。然而，模拟结果显示，在L~10^10h^-2Lsun处，β最小值的位置与M/L最小值的位置之间存在系统性的偏移，这是通过使用已知的DM分布直接计算得出的。我们的总体结论是，从动力学下降的偏见估计似乎支持在中间晕质量的恒星形成效率的最小值。尽管如此，使用大尺度入流测量β 1/b而不是使用小尺度速度弥散测量M/L，仍可能产生重大的系统问题。
英文摘要：
Prompted by indications from QSO lensing that there may be more mass associated with galaxy groups than expected, we have made new dynamical infall estimates of the masses associated with 2PIGG groups and clusters. We have analysed the redshift distortions in the cluster-galaxy cross-correlation function as a function of cluster membership, cross-correlating z<0.12 2PIGG clusters and groups with the full 2dF galaxy catalogue. We have made estimates of the dynamical infall parameter beta and new estimates of the group velocity dispersions. We first find that the amplitude of the full 3-D redshift space cross-correlation function, xi_{cg}, rises monotonically with group membership. We use a simple linear-theory infall model to fit xi(sigma, pi) in the range 5<s<40h^{-1}Mpc. We find that the beta versus membership relation for the data shows a minimum at intermediate group membership n~20 or L~2x10^11h^-2Lsun, implying that the bias and hence M/L ratios rise by a significant factor (~5x) both for small groups and rich clusters. However, the mocks show a systematic shift between the location of the beta minimum and the M/L minimum at L~10^10h^-2Lsun given by direct calculation using the known DM distribution. Our overall conclusion is that bias estimates from dynamical infall appear to support the minimum in star-formation efficiency at intermediate halo masses. Nevertheless, there may still be significant systematic problems arising from measuring beta~1/b using large-scale infall rather than M/L using small-scale velocity dispersions.
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