Multivariate Analysis

The two multivariate analyses we performed on this sample are: (1) tree--clustering; and (2) K--means clustering. Briefly, tree clustering looks at how QSOs are clustered in parameter space by iteratively computing distances between object pairs and replacing the two closest objects with a single object. (Here, object refers either to a QSO or a group of QSOs.) From the diagram, the QSOs cluster in five clear groups. One of the groups (group 4), is completely devoid of NALs implying that the properties that characterize this group seriously inhibit the production of NAL gas.