Retorne
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.