The central engines of narrow-line Seyfert 1 galaxies.
RYAN C.J., DE ROBERTIS M.M., VIRANI S., LAOR A. and DAWSON P.C.
Abstract (from CDS):
It has been suggested that narrow-line Seyfert 1 galaxies (NLS1s) are evolutionarily young objects, powered by accretion onto central black holes that are significantly lower in mass than those found in typical broad-line Seyfert galaxies. We explore this hypothesis through the analysis of high spatial resolution, near-IR imaging data. By employing the correlation between black hole mass and host galaxy bulge luminosity, we determine the mean black hole mass for our sample to be, in solar units, <log(MBH)≥7.9. Using the correlation between the size of the broad-line region and the monochromatic continuum luminosity, we obtain black hole mass estimates under the assumption that the emission-line gas is in virial equilibrium. The mean black hole mass derived from this relation is <log(MBH)≥6.4. We explore possible causes for this discrepancy in MBHestimates and the ramifications for our understanding of the role played by NLS1s in AGN evolution. Because numerical simulations constrain the start of the AGN duty cycle to a time shortly after a gravitational interaction, we examine the morphology and near-IR bulge colors of the NLS1 sample for evidence of recent encounters. The mean bulge color is found to be redder than that of both a matched sample of nonactive galaxies and published estimates for broad-line Seyfert galaxies. The source of the unusual bulge colors may be an excess of flux, peaking at 2.2 µm, that has been detected near the centers of some NLS1s. No evidence is found for light asymmetries or an extra stellar component that would indicate NLS1s are young objects. Finally, we postulate that there may be some interesting lines of circumstantial evidence suggesting that secular processes may be relevant in NLS1s.