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(Hβ) 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. The Eddington ratio L/L_Edd correlates with the X-ray spectral index α_X and the black home mass M_BH anticorrelates with the X-ray variability χ²/ν. 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.

Based in part on observations at the European Southern Observatory La Silla (Chile) with the 2.2 m telescope of the Max Planck Society during MPI and ESO time and the ESO 1.52 m telescope during ESO time in 1995 September and 1999 September.