What drives the Quasar Main Sequence?

Original · EN

Eigenvector 1 (EV1) was found to be the dominant component behind the significant correlations for the measured parameters in quasar spectra (Boroson & Green, 1992). The parameter RFeII, which strongly correlates to the EV1, is the FeII strength, defined to be the ratio of the equivalent width of FeII to the equivalent width of Hβ. This allows to construct a quasar main sequence analogous to the stellar properties driven HR diagram (Sulentic et al. 2001). We try to find the main driver behind the EV1 among the basic (theoretically motivated) parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle). Based on theoretical modeling using the photoionization code CLOUDY (Ferland et al. 2013), we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature (TBBB), reflected in the shape of the spectral energy distribution (SED). We have assumed that both Hβ and FeII emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We test the effect of changing Eddington ratio on the RFeII - TBBB trends with varying mean hydrogen densities. We also test the effect of adding microturbulence that affect the line intensities on the overall RFeII - TBBB picture.