The Case for Two Quasar Populations

Abstract

We present evidence for two populations of quasars showing distinctly different broad line structure and kinematics. The first evidence for quasar dichotomy involve differences between radio-quiet and radio-loud sources. We proposed an alternate population A-B dichotomy based on optical, UV and X-ray spectroscopic properties. One of these populations (Pop. A: FWHM Hβ 4000 kms-1) includes most radio-loud sources and a significant number of spectroscopically indistinguishable (as far as the low-ionization lines are concerned) radio-quiet sources. Comparison of multiwavelength measures for population A and B sources reveals more/larger differences than are found between radioquiet and radio-loud sources leading us to conclude that the population A-B distinction is more fundamental. The major physical driver of these differences is likely the Eddington ratio where the Pop. A sources show log L/LEdd = 0.2-1.0, and the Pop. B sources show log L/LEdd = 0.01-0.2 (for black hole masses logMBH ≈ 8.5).

Keywords

• quasars
• general quasars
• emission lines