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Empirical diagnostics of the starburst-AGN connection

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Empirical diagnostics of the starburst-AGN connection

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Título Empirical diagnostics of the starburst-AGN connection
Autor Fernandes Junior, Roberto Cid
Heckman, Timothy M.
Schmitt, Henrique Roberto
González Delgado, Rosa M.
Storchi-Bergmann, Thaisa
Abstract We examine a representative sample of 35 Seyfert 2 nuclei. Previous work has shown that nearly half (15) of these nuclei show the direct (but difficult to detect) spectroscopic signature at optical/near-UV wavelengths of the hot massive stars that power circumnuclear starbursts. In the present paper we examine a variety of more easily measured quantities for this sample, such as the equivalent widths of strong absorption features, continuum colors, emission line equivalent widths, emission line ratios and proÐles, far-IR luminosities, and near-UV surface brightness. We compare the composite starburst + Seyfert 2 nuclei to "pure" Seyfert 2 nuclei, Starburst galaxies, and normal galactic nuclei. Our goals are to verify whether the easily measured properties of the composite nuclei are consistent with the expected impact of a starburst and to investigate alternative less demanding methods to infer the presence of starbursts in Seyfert 2 nuclei, applicable to larger or more distant samples. We show that starbursts do indeed leave clear and easily quantiÐable imprints on the near-UV to optical continuum and emission line properties of Seyfert 2's. Composite starburst + Seyfert 2 systems can be recognized by: (1) a strong "featureless continuum" (FC), which dilutes the Ca II K line from old stars in the host's bulge to an equivalent width WK<10 Å; (2) emission lines whose equivalent widths are intermediate between starburst galaxies and "pure" Seyfert 2's ; (3) relatively low excitation line ratios, which indicate that part of the gas ionization in these Seyfert 2's (typically ~50% of Hβ) is due to photoionization by OB stars ; (4) large far-IR luminosities (>~10 10 Lʘ; (5) high near-UV surface brightness (~10 3 Lʘ pc-²). These characteristics are all consistent with the expected impact of circumnuclear starbursts on the observed properties of Seyfert 2's. Furthermore, they o†er alternative empirical diagnostics of the presence of circumnuclear starbursts from a few easily measured quantities.
Contido em The astrophysical journal. Chicago. Vol. 558, no. 1 pt. 1 (Sept. 2001), p. 81-108
Assunto Espectros astronômicos
Fontes de infravermelho
Formacao de estrelas
Fotometria astronômica
Galaxias seyfert
Materia interestelar
Nucleo galatico
[en] Galaxies : nuclei
[en] Galaxies : Seyfert
[en] GHalaxies : active
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/108884
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