The Origin of σ–drops: Mapping Stellar Kinematics and Populations in Spirals

The link between nuclear activity and the host galaxy remains elusive. It seems now clear that the galactic environment is not the key, and that there is no significant apparent difference in terms of the presence of bars/spirals between active and non-active galaxies. Nuclear activity nevertheless requires a small central gas reservoir (10-10 M ) which may be only partly consumed during the ∼ 10 − 10 yr AGN duty cycle. A possible route towards a better understanding of the involved physical processes is to directly probe the gravitational potential of the host galaxies, with the hope that the corresponding sensitive tracers (stars, gas) will deliver convincing evidence for a kinematic signature associated with the AGN. This is the motivation for an on-going survey of 50 galaxies, for which the two-dimensional kinematics of the (neutral, ionised and molecular) gas and stellar components are being obtained (see Dumas et al., this conference). With only 10 to 15% of Seyfert galaxies in the local Universe, we must also acknowledge the possibility that this activity is a recurrent (but short) process, and that signatures of recent gas accretion associated with the onset of the central activity should be detectable. This paper is a short report on the detection and study of σ–drops which we believe are the result of past gas accretion followed by subsequent star formation.