The Host Galaxies of Nearby Seyfert 1 Nuclei

Abstract

We use optical and infrared imaging data of a complete hard X-ray selected sample of AGN to investigate the host galaxies of nearby Seyfert 1 nuclei. We disentangle the emission due to the unresolved point source and the resolved host galaxy by means of luminosity profile fitting. The stellar colours in the nucleus are redder in B — V and V — K than in normal spiral bulges or current stellar evolutionary models, probably due to dust obscuration. J — H colour is quite normal but H — K usually very red, probably indicating a large contribution from reradiating hot dust to the IR colours. No significant difference in IR colours of the stellar component is found with respect to a comparison sample of Liners and starbursts, except that the reradiating dust in Seyferts tends to be hotter and lie closer to the nucleus. B — V colour gets slightly bluer towards the nucleus, whereas V — K and J — K have red gradients. B — V and J — K gradients are not correlated and are likely to be caused by different mechanisms. There is a clear correlation between the AGN and host luminosity. Finally, we present optical colour ratio maps of two Seyfert nuclei, NGC 3227 and NGC 7469. The blue, ringlike or elongated structure in the maps and its correspondence with molecular CO geometry is interpreted as evidence for circumnuclear star formation in these AGN.