Dynamics of embedded bars and the connection with AGN

Abstract

We present new stellar kinematical profiles of four galaxy hosts of active galactic nuclei, using the 12 CO bandhead around 2.3 µm with the ISAAC/VLT spec- trograph. We find that the nuclear bars or discs, em- bedded in large-scale primary bars, have all a decoupled kinematics, in the sense that the maximum of the rota- tional velocity occurs in the nuclear region. In three cases (NGC 1097, NGC 1808 and NGC 5728), the velocity dis- persion displays a significant drop at the nucleus, a rarely observed phenomenon. We also detect kinematical asym- metries (m = 1 mode) along the nuclear bar major-axis of NGC 1808 and NGC 5728, dynamical counterparts of corresponding asymmetries in the surface brightness. We have derived simple dynamical models in an attempt to fit the kinematics of each galaxy and reconstruct the full velocity field. For all four targets, the fits are good, and confirm the presence of the decoupled nuclear components. These models cannot however reproduce the observed cen- tral drop in the dispersion. We suggest that this drop is due to a transient cold nuclear disc, fuelled by gas inflow along the bar, that has recently formed new stars.