A complete sample of soft X-ray-selected AGNs. II. Statistical analysis

Direct correlations and a principal component analysis (PCA) are presented for a complete sample of 110 soft X-ray-selected AGNs, of which about half are narrow-line Seyfert 1 galaxies (NLS1's). The direct correlation analyses show that narrower FWHM(Hbeta) correlates with steeper X-ray spectrum, stronger optical Fe II emission, weaker [O III] emission and stronger short-term X-ray variability. This direct correlation analysis and the PCA confirm the Boroson & Green ( 1992) eigenvector 1 relationship for AGNs: Fe II strength anticorrelates with [ O III] line strength. Eigenvector 1 is well correlated with the Eddington luminosity ratio L/L-Edd, while eigenvector 2 shows a very good correlation with the mass of the central black hole M-BH and the mass accretion rate (M) over dot. . The Eddington ratio L/L-Edd correlates with the X-ray spectral index alpha(X) and the black home mass M-BH anticorrelates with the X-ray variability chi(2)/nu. The Eddington ratio L/L-Edd may be interpreted as the age of an AGN: AGNs with steep X-ray spectra, strong Fe II, and weak [O III] are AGNs in an early phase of their evolution. In this hypothesis, NLS1's are young AGNs.