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MINI REVIEW article

Front. Astron. Space Sci.
Sec. Extragalactic Astronomy
Volume 11 - 2024 | doi: 10.3389/fspas.2024.1479874
This article is part of the Research Topic Frontiers in Astronomy and Space Sciences: A Decade of Discovery and Advancement - 10th Anniversary Conference View all 3 articles

Unveiling The Quasar Main Sequence: Illuminating The Complexity Of Active Galactic Nuclei And Their Evolution

Provisionally accepted
Swayamtrupta Panda Swayamtrupta Panda 1,2*
  • 1 Gemini Observatory, La Serena, Chile
  • 2 Laboratório Nacional de Astrofí­sica, Itajubá, Brazil

The final, formatted version of the article will be published soon.

    The Eigenvector 1 schema, or the main sequence of quasars, was introduced as an analogous scheme to the HR diagram that would allow us to understand the more complex, extended sources -active galactic nuclei (AGNs) that harbor accreting supermassive black holes. The study has spanned more than three decades and has advanced our knowledge of the diversity of Type-1 AGNs from both observational and theoretical aspects. The quasar main sequence, in its simplest form, is the plane between the FWHM of the broad Hβ emission line and the strength of the optical FeII emission to the Hβ. While the former allows the estimation of the black hole mass, the latter enables direct measurement of the metal content and traces the accretion rate of the AGN. Together, they allow us to track the evolution of AGN in terms of the activity of the central nuclei, its effect on the line-emitting regions surrounding the AGN, and their diversity making them suitable distance indicators to study the expansion of our Universe. This mini-review aims to provide (i) a brief history leading up to the present day in the study of the quasar main sequence, (ii) introduce us to the many possibilities to study AGNs with the main sequence as a guiding tool, and (iii) highlight some recent, exciting lines of researches at the frontier of this ever-growing field.

    Keywords: active galactic nuclei, quasars, Seyfert galaxies, emission lines, AGN variability, changing-look AGNs, accretion disks

    Received: 12 Aug 2024; Accepted: 09 Sep 2024.

    Copyright: © 2024 Panda. 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) or licensor 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: Swayamtrupta Panda, Gemini Observatory, La Serena, Chile

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