THE HOST GALAXIES OF SEYFERT TYPE-1 NUCLEI

This paper is part of a eries in which we study a hard-X-rav-selected sample of AGN, mainly optically classified as Seyfert 1 nuclei. In thi s paper, we use our optical and infrared imaging data of the sample to study the properties of the host galaxies. We separate the non-stella r and stellar components of the nuclear light, on the basis of the res ults from Papers I and III. The stellar colours in the nucleus are gen erally much redder in B - V and V - K indices than normal spiral galax y bulges, and can be reproduced using stellar evolution models modifie d by approximately 1 mag of reddening in A(V) and/or reradiation from hot dust. The J - H colour is normal, but H - K is usually very red, i ndicating that the near-infrared (NIR) colours are affected by dust re radiation within the K band, either heated by the active nucleus or by young stars in H II regions associated with enhanced star formation a round the nucleus. The NIR colours are similar to those observed in a sample of starburst/LINER galaxies. The B - V, V - K and J - K colours have red gradients towards the nucleus, although there is considerabl e scatter. The B - V and J - K colour gradients are not correlated, an d are therefore likely to be caused by different mechanisms. The colou r gradients are in good agreement with those seen in normal spiral gal axies. We present luminosity distributions of the host galaxies in B, V, J and K. There is a strong correlation between the AGN and the host galaxy luminosity, in the sense that the more powerful AGN reside in more luminous host galaxies. The luminosities of the host galaxies for our sample fall between those of normal spiral galaxies and the hosts of quasars. The central surface brightnesses and the length scales of the discs are not well determined from the decomposition fits, but on average they are consistent with values found in previous studies.