Nuclear activity and star formation properties of Seyfert 2 galaxies
  In order to characterize the amount of recent or ongoing stellar formation in
the circumnuclear region of active galaxies on a statistically sound basis, we
have studied the stellar component of the nuclear spectra in three different
samples of galaxies, namely Seyfert 2 galaxies (hereafter S2G), star-forming
galaxies (SFG) and passive normal galaxies (NG), i.e., no emission lines
observed, using Sloan Digital Sky Survey data (SDSS) (Adelman-McCarthy, 2008).
The stellar component of the observed spectra has been extracted using
STARLIGHT (Cid Fernandes et al., 2004), which fits an observed spectrum with a
model (template) spectrum obtained by combining a library of pre-defined simple
stellar populations spectra, with distinct ages and metallicities. The
resulting template spectra for the different samples of galaxies have been
compared to determine the features of the stellar emission component and to
evaluate the presence and intensity of the star formation in the nuclear
regions of different families of galaxies. From a first qualitative analysis it
results that the shape of the Spectral Energy Distribution (SED) of S2G and NG
is very similar, while that of SFG is characterized by a strong blue excess.
The presence of the 4000 A break in the spectra of S2G and NG together with the
lack of a strong blue continuum clearly indicate the absence of ongoing star
formation in the circumnuclear regions of S2G and obviously of NG. Anyway
traces of a recent star formation history are evident in the spectra of S2G
galaxies, which show a 4000 A break systematically shallower than in NG.
