Mon. Not. R. Astron. Soc., 400, 273-290 (2009/November-3)
Probing the near-infrared stellar population of Seyfert galaxies.
RIFFEL R., PASTORIZA M.G., RODRIGUEZ-ARDILA A. and BONATTO C.
Abstract (from CDS):
We employ Infrared Telescope Facility SpeX near-infrared (NIR; 0.8-2.4 µm) spectra to investigate the stellar population (SP), active galactic nuclei (AGN) featureless continuum (FC) and hot dust properties in nine Sy1 and 15 Sy2 galaxies. Both the starlight code and the hot dust as an additional base element were used for the first time in this spectral range. We found evidence of correlation among the equivalent widths (Wλ) Sii1.59 µmxMgi1.58 µm, equally for both kinds of activity. Part of the WNaI2.21µm and WCO2.3µmstrengths may be related to galaxy inclination. Our synthesis shows significant differences between Sy1 and Sy2 galaxies: the hot dust component is required to fit the K-band spectra of ∼90 per cent of the Sy1 galaxies, and only of ∼25 per cent of the Sy2; about 50 per cent of the Sy2 galaxies require an FC component contribution ≳20 per cent, while this fraction increases to about 60 per cent in the Sy1; also, in about 50 per cent of the Sy2, the combined FC and young components contribute with more than 20 per cent, while this occurs in 90 per cent of the Sy1, suggesting recent star formation in the central region. The central few hundred parsec of our galaxy sample contain a substantial fraction of intermediate-age SPs with a mean metallicity near solar. Our SP synthesis confirms that the 1.1 µm CN band can be used as a tracer of intermediate-age SPs. The simultaneous fitting of SP, FC and hot dust components increased in ∼150 per cent the number of AGNs with hot dust detected and the mass estimated. The NIR emerges as an excellent window to study the SP of Sy1 galaxies, as opposed to the usually heavily attenuated optical range. Our approach opens a new way to investigate and quantify the individual contribution of the three most important NIR continuum components observed in AGNs.