الفهرس 
Title : Statistical and observational study of some galaxy groups
AbstractOnly 14 pages are availabe for public view
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Abstract
This thesis deals with a statistical study of small galaxy groups (quintets). The study of galaxy groups is a key in understanding galactic evolution as well as the structure of the Universe. In this thesis, I make use of the similarity of colour indices (u-g) and (g-r) between group members in the nearby Universe (z {u2264} 0.2) to confirm their membership and to detect the outlier galaxies. I used an algorithm based on the Euclidean distance as a similarity measure with built-in outlier removal criteria. The algorithm is applied on two samples of quintet galaxy groups, (i) Compact groups from (Lee et al. 2004). (ii) Loose groups from (Tempel et al. 2014). I found that 32 % of the chosen compact groups have outliers while this percentage reduced to 27 % for the sample of loose groups. I compared the luminosity of the outlier galaxies with the confirmed members. The results showed that member galaxies are more luminous than the outliers. I conclude that galaxies have environmental colour dependence and consequently their colour similarity give a better identification of galaxy group membership in the nearby Universe. Therefore, colour similarity can be used as a criterion of defining members of galaxy groups