A Main Sequence for Quasars

Abstract

The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called "main sequence" associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

Quasar Black Hole Mass Estimates from High-Ionization Lines: Breaking a Taboo?

“…All symmetrization methods were found to be equivalent at low-and high-L [45]. In other words, the Hβ profile shapes at high L are consistent with those at low-z, lower L (with some caveats, [11]).…”

“…The physical origin of this behavior is not yet clear: in principle, shielding, optically thin gas, changing size of the continuum source could also give rise to a shorter (or a lack of) response to continuum change in the emitting line regions. In addition, periodic signals (in photometric and spectroscopic measurements) have been detected in a number of sources [40], including NGC 5548 (e.g., [41][42][43][44][45]). The origin of the periodicity is as yet unclear as well.…”

“…A scaling law that assumes M BH ∝ FWHM 0.5 [32] accounts for the over-broadening of Population A sources, but overcorrects for Population B [45]. In general, corrections dependent on L/L Edd (which is correlated with FWHM of CIV, [85]) or an L/L Edd proxy such as the SiIV + OIV]1400 blend/CIV 1549 ratio are promising [9] but tend not to work well for Population B. Empirical corrections based on CIV blueshift work fairly well for high-L sources only [83,86].…”

“…Population B sources at low Eddington ratio require a different correction (still ill-defined by the analysis of Marziani et al [45] as Population B sources are most affected by the Eddington ratio bias mentioned in Section 5.3).…”

“…Author Contributions: This review is partly based on the results of several research papers by the authors: [45,76] (A.N. ), [12,13,45] (A.D.O.…”