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Emission-Line Taxonomy and the Nature of AGN-Looking Galaxies in the SDSS

Published online by Cambridge University Press:  03 June 2010

Roberto Cid Fernandes
Affiliation:
Departamento de Física-CFM, Universidade Federal de Santa Catarina, Florianópolis, Brazil
Grażyna Stasińska
Affiliation:
LUTH, Observatoire de Paris-Meudon, France
Natalia Vale Asari
Affiliation:
Departamento de Física-CFM, Universidade Federal de Santa Catarina, Florianópolis, Brazil
Abílio Mateus
Affiliation:
Departamento de Física-CFM, Universidade Federal de Santa Catarina, Florianópolis, Brazil
Marielli S. Schlickmann
Affiliation:
Departamento de Física-CFM, Universidade Federal de Santa Catarina, Florianópolis, Brazil
William Schoenell
Affiliation:
Departamento de Física-CFM, Universidade Federal de Santa Catarina, Florianópolis, Brazil
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Abstract

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Massive spectroscopic surveys like the SDSS have revolutionized the way we study AGN and their relations to the galaxies they live in. A first step in any such study is to define samples of different types of AGN on the basis of emission-line ratios. This deceivingly simple step involves decisions on which classification scheme to use and data quality censorship. Galaxies with weak emission lines are often left aside or dealt with separetely because one cannot fully classify them onto the standard star-forming, Seyfert, or LINER categories. This contribution summarizes alternative classification schemes which include this very numerous population. We then study how star-formation histories and physical properties of the hosts vary from class to class, and present compelling evidence that the emission lines in the majority of LINER-like systems in the SDSS are not powered by black-hole accretion. The data are fully consistent with them being galaxies whose old stars provide all the ionizing power needed to explain their line ratios and luminosities. Such retired galaxies deserve a place in the emission-line taxonomy.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2010

References

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