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This article is part of the Research Topic

Quasars at all cosmic epochs

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Front. Astron. Space Sci. | doi: 10.3389/fspas.2018.00006

A main sequence for quasars

  • 1Osservatorio Astronomico di Padova (INAF), Italy
  • 2Instituto de Astronomía, Universidad Nacional Autonoma de Mexico, Mexico
  • 3Instituto de Astrofísica de Andalucía (CSIC), Spain
  • 4Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Italy
  • 5ASTRONOMICAL OBSERVATORY BELGRADE, Serbia
  • 6Osservatorio astronomico di Bologna (INAF), Italy

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.

Keywords: Galaxy evolution, quasars, Eigenvector 1, Outflows, emission lines, Supermassive black holes, black hole physics, accretion disk

Received: 17 Oct 2017; Accepted: 07 Feb 2018.

Edited by:

Sandor M. Molnar, National Taiwan University, Taiwan

Reviewed by:

Shai Kaspi, Tel Aviv University, Israel
Gordon Richards, Drexel University, United States  

Copyright: © 2018 Marziani, Dultzin, Sulentic, Del Olmo, Negrete, Martínez-Aldama, D'Onofrio, Bon, Bon and Stirpe. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Paola Marziani, Osservatorio Astronomico di Padova (INAF), Padua, Italy, paola.marziani@oapd.inaf.it