【摘要】 本文提出一种以视向速度为判据,按最大似然原理确定星系团成员的统计方法.所用的数学模型认为团星系视向速度服从一维正态分布,场星系服从K个一维正态分布,它们彼此重迭.对COMA星系团的成员研究表明,这一数学模型是合理的,可以很好地确定星系团的分布参数和各别星系的成员概率,成员判别十分有效.当K=2,即把场星系分别作为前景星系和背景星系来考虑时,可望得到更好的结果.另外,至少在样本不很大时,K>2是不可取的.更多还原

【Abstract】 Determination of membership is of importance for studies on clusters of galaxies. Membership in clusters has usually been assigned on the basis of location and apparent magnitude and recently radial velocity and colour criteria are also used, but no mathematical model has been yet established for membership study. Based upon the maximum likelihood principle, a statistical method used for membership deter mination of clusters of galaxies from data of radial velocities is developed in this paper. The mathematical model which the method is based on is to assume that radial velocitis of cluster members follow an one-dimensional normal distribution and those of field galaxies follow k one-dimensional normal distributions, these distributions being overlapped with each other. Using the list of redshifts for 414 galaxies in the sky region of Coma cluster compiled by Kent and Gunn, we have made a membership study for the cluster, and obtained the distribution parameters of the cluster and membership probabilities of individual galaxies in the sample, separately for k=1 or K=2 and R<3° or R<6°, where R is the angular distance of a galaxy from the cluster center. It is concluded from detailed discussions that: （1） The mathematical model developed is resanable and effective, which can be used to determine the distribution parameters and membership probablities, discrimination between cluster members and field galaxies being satisfacory. （2） Results on determination of membership seem to be the best when K=2, i.e. field galaxies are considered as foreground ones and background ones separately. For K=2 and R<3° we find the mean radial velocity and the radial velocity dispersion of the Coma cluster are v_c=6930+60km s^-1 and σ_c=840+50km s^-1 correspondingly. （3） A value of K larger than 2 seems to be unpreferable, at least for the cases of not big enough samples. We have found for the Coma cluster that the distribution parameters did not converge or converged to some unrealistic values when K=3 or 4. （4） The distribution parameters obtained for samples of galaxies with R<3° and R<6° are not significantly different. The radial velocity dispersion of cluster members for the sample with R<3° is bigger than that for the sample with R<6°.更多还原