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Emission Line Diagnostics

Published online by Cambridge University Press:  23 November 2009

By
Hagai Netzer
Edited by
Robert Williams  and
Mario Livio
Hagai Netzer
Affiliation:
School of Physics and Astronomy and the Wise Observatory, Tel Aviv University
Robert Williams
Affiliation:
Space Telescope Science Institute, Baltimore
Mario Livio
Affiliation:
Space Telescope Science Institute, Baltimore
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Summary

This review focus on three major aspects of emission line diagnostics: Line intensities that are used to deduce the physical conditions in the gas, line profiles that are needed to study the gas dynamics, and line variability, that is used to obtain the gas distribution. Applications and examples are given for active galaxies and quasars. The status of research and the outstanding problems in each of these areas are discussed and new observational findings are shown. The more important developments of recent years are due to systematic, combined space and groundbased observations of individual objects (reverberation mapping) as well as studies of large samples of AGNs (e.g. the HST radio-loud sample).

Introduction and overview of active galactic nuclei

Observations of emission lines in photoionized nebulae provide important diagnostics of the line emitting gas in three different ways: Line intensities are used to derive the physical conditions in the gas. Density, temperature, optical depth etc. are all related to emission line ratios and absolute fluxes. Line profiles are used to investigate the gas dynamics and the velocity field. Finally, line variability, when correlated with flux variations of the photoionizing continuum, are used to measure the gas distribution and the size of the emission line region.

Active Galactic Nuclei (AGN) are situated in the center of otherwise normal galaxies and show strong emission lines superimposed on strong nonstellar continua.

Type
Chapter
Information
The Analysis of Emission Lines , pp. 97 - 106
Publisher: Cambridge University Press
Print publication year: 1995

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  • Emission Line Diagnostics
    • By Hagai Netzer, School of Physics and Astronomy and the Wise Observatory, Tel Aviv University
  • Edited by Robert Williams, Space Telescope Science Institute, Baltimore, Mario Livio, Space Telescope Science Institute, Baltimore
  • Book: The Analysis of Emission Lines
  • Online publication: 23 November 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600180.009
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  • Emission Line Diagnostics
    • By Hagai Netzer, School of Physics and Astronomy and the Wise Observatory, Tel Aviv University
  • Edited by Robert Williams, Space Telescope Science Institute, Baltimore, Mario Livio, Space Telescope Science Institute, Baltimore
  • Book: The Analysis of Emission Lines
  • Online publication: 23 November 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600180.009
Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Emission Line Diagnostics
    • By Hagai Netzer, School of Physics and Astronomy and the Wise Observatory, Tel Aviv University
  • Edited by Robert Williams, Space Telescope Science Institute, Baltimore, Mario Livio, Space Telescope Science Institute, Baltimore
  • Book: The Analysis of Emission Lines
  • Online publication: 23 November 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600180.009
Available formats
×