Gas and stellar dynamics in NGC 1068. Probing the galactic gravitational potential

We present SAURON integral field spectrography of the central 1.5 kpc of the nearby Seyfert 2 galaxy NGC 1068, encompassing the well-known near-infrared inner bar observed in the K band. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their two-dimensional distribution and kinematics. The [Oiii] and Hβ emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hβ and [Oiii] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and Gauss-Hermite h3 fields. We re-examined the long-slit data of Shapiro et al. (2003) using a penalized pixel fitting routine: a strong decoupling of the Gauss-Hermite term h3 is revealed, and the central decrease of Gauss-Hermite term h4 hinted in the SAURON data is confirmed. These data also suggest that NGC 1068 is a good candidate for a so-called σ-drop. We confirm the possible presence of two separate pattern speeds applying the Tremaine-Weinberg method to the Fabry-Perot Hα map (Bland-Hawthorn et al. , 1991). We also examine the stellar kinematics of bars formed in N-body + SPH simulations built from axisymmetric initial conditions approximating the luminosity distribution of NGC 1068. The resulting velocity, dispersion, and higher order Gauss-Hermite moments successfully reproduce a number of properties observed in the two-dimensional kinematics of NGC 1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are likely mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models nevertheless suggest that the inner bar could drive a significant amount of gas down to a scale of ∼ 300 pc. This would be consistent with the interpretation of the σ-drop in NGC 1068 being the result of central gas accretion followed by an episode of star formation.