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Título               : Empirical diagnostics of the starburst-AGN connection  
Conferencista: Roberto Cid Fernandes Junior, FSC/UFSC  
Data                  : Sexta-feira, 04/05/01 15H30M  
Local                 : Auditório L.B.F. Clauzet - Água Funda  
Sumário           :
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 circum-nuclear 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 profiles, 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 quantifiable 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 CaII K line from old stars in the host's bulge to an equivalent width $W_K < 10$ \AA; (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 $\sim 50\%$ of H$\beta$) is due to photoionization by OB stars; (4) large far IR luminosities ($\ga 10^{10}$ L$_\odot$); (5) High near-UV surface brightness ($\sim 10^3$ L$_{\odot}$ pc$^{-2}$). These characteristics are all consistent with the expected impact of circum-nuclear starbursts on the observed properties of Seyfert 2's. Furtheremore, they offer alternative empirical diagnostics of the presence of circum-nuclear starbursts from a few easily measured quantities.