2013A&A...556A.136I

We present H- and K-band data from the inner arcsecond of the Seyfert 1.5 galaxy NGC 4151 obtained with the adaptive-optics-assisted near-infrared-imaging field spectrograph OSIRIS at the Keck Observatory. The angular resolution is about a few parsecs on-site and thus competes easily with optical images taken previously with the Hubble Space Telescope. We present the morphology and dynamics of most species detected but focus on the morphology and dynamics of the narrow line region (as traced by emission of [FeII]λ1.644µm), the interplay between plasma ejected from the nucleus (as traced by 21cm continuum radio data) and hot H₂ gas and characterize the detected nuclear HeIλ2.058µm absorption feature as a narrow absorption line (NAL) phenomenon. The emission from the narrow line region (NLR) as traced by [FeII] reveals a biconical morphology and we compare the measured dynamics in the [FeII] emission line with models that propose acceleration of gas in the NLR and simple ejection of gas into the NLR. In the inner 2.5-arcsec the acceleration model reveals a better fit to our data than the ejection model. We also see evidence that the jet very locally enhances emission in [FeII] at certain positions in our field-of-view such that we were able to distinct the kinematics of these clouds from clouds generally accelerated in the NLR. Further, the radio jet is aligned with the bicone surface rather than the bicone axis such that we assume that the jet is not the dominant mechanism responsible for driving the kinematics of clouds in the NLR. The hot H₂ gas is thermal with a temperature of about 1700K. We observe a remarkable correlation between individual H₂ clouds at systemic velocity with the 21cm continuum radio jet. We propose that the radio jet is at least partially embedded in the galactic disk of NGC 4151 such that deviations from a linear radio structure are invoked by interactions of jet plasma with H₂ clouds that are moving into the path of the jet because of rotation of the galactic disk of NGC 4151. Additionally, we observe a correlation of the jet as traced by the radio data, with gas as traced in Brγ and H₂, at velocities between systemic and ±200km/s at several locations along the path of the jet. The HeIλ2.058µm line in NGC 4151 appears in emission with a blueshifted absorption component from an outflow. The emission (absorption) component has a velocity offset of 10km/s (-280km/s) with a Gaussian (Lorentzian) full-width (half-width) at half maximum of 160km/s (440km/s). The absorption component remains spatially unresolved and its kinematic measures differ from that of UV resonance absorption lines. From the amount of absorption we derive a lower limit of the HeI 2¹S column density of 1x10¹⁴cm^–2 with a covering factor along the line-of-sight of C_los≃0.1.