Abstract

We present here the analysis of morphological and photometric properties of a sample of isolated spirals with (18) and without (11) an active nucleus, based on near-infrared imaging in the J and K' bands (Paper I). The aim of that comparative analysis is to find the differential properties that could be directly connected with the phenomenon of nuclear activity. We stress the importance of using isolated objects for that purpose. Our study shows that both sets of galaxies are similar in their global properties: they define the same Kormendy relation, their disk components share the same properties, the bulge and disk scale lengths are correlated in a similar way, bar strengths and lengths are similar for primary bars. Our results therefore indicate that hosts of isolated Seyfert galaxies have bulge and disk properties comparable to those of isolated non active spirals. Central colors (the innermost 200 pc) of active galaxies are redder than the centers of non active spirals, most probably due to AGN light being re-emitted by the hot dust and/or due to circumnuclear star formation, through the contribution of giants/supergiants. Central to our analysis is the study of the possible connection between bars and similar non axisymmetric structures with the nuclear fuelling. We note that only one of the Seyfert galaxies in our sample, namely ESO 139-12, does not present a primary bar. But bars are equally present in active and control objects. The same applies to secondary bars. Not all the active galaxies we have observed have them, and some control galaxies also present such central structures. Secondary central elongations (associated with secondary bars, lenses, rings or disks) may be somewhat different, but this result should be confirmed with larger samples. We note that numerical models indicate that such secondary bars are not strictly necessary to feed the central engine when a primary bar is present. Our results show that down to scales of 100-300 pc, there are no evident differences between active and non active spiral galaxies. Based on data obtained at: the European Southern Observatory, La Silla, Chile, the Télescope Bernard Lyot, Calar Alto Observatory, Las Campanas Observatory. Also based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space --- II. Photometric properties of the host galaxies.