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Paper: The Stellar Populations of Seyfert 2 Nuclei
Volume: 373, The Central Engine of Active Galactic Nuclei
Page: 643
Authors: Sarzi, M.; Shields, J.C.; Pogge, R.W.; Martini, P.
Abstract: We present a preliminary analysis of the stellar populations in the central parsecs of a sample of 22 Seyfert 2 galaxies, based on a careful separation of nebular emission and stellar light in high-spatial resolution HST-STIS spectra. 10% of the surveyed nuclei display stellar populations of intermediate age, ~12 Gyr old, whereas the remaining targets appear to be evenly split between objects showing only very old stellar populations and nuclei requiring also an additional blue featureless component, which we characterize by means of very young, few Myr-old stars. The small fraction of stellar population of intermediate age seems to argue against the presence of such a young component, however, since the short lifetime of O stars would imply recurrent star formation episodes and the build-up over the last 12 Gyr of an easily detectable intermediate-age population. Additionally, a tight relation between the luminosity of such a blue component and the emission from highly ionized species further suggests that the featureless continuum arises from the central engine rather than from star-forming regions. We discuss our results in the framework of the unification paradigm and of models for star formation in the immediate vicinity of supermassive black holes.
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