Volume 556, August 2013
|Number of page(s)||27|
|Published online||08 August 2013|
Near-infrared imaging spectroscopy of the inner few arcseconds of NGC 4151 with OSIRIS at Keck⋆
Physikalisches Institut, Universität zu Köln,
Zülpicher Strasse 77,
2 Deutsches SOFIA Institut, Universität Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
3 Division of Astronomy, University of California, Los Angeles, CA 90095-1562, USA
4 University of Rochester, Laboratory for Laser Energetics, PO Box 278871, Rochester, NY 14627-8871, USA
5 Exoplanets and Stellar Astrophysics Laboratory, Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
6 Landessternwarte, Zentrum fr Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
7 Dunlap Institute for Astronomy & Astrophysics, 50 St. George Street, Toronto, ON, M5S 3H4, Canada
Accepted: 18 March 2013
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]λ1.644 μm), the interplay between plasma ejected from the nucleus (as traced by 21 cm continuum radio data) and hot H2 gas and characterize the detected nuclear HeIλ2.058 μm 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 1700 K. We observe a remarkable correlation between individual H2 clouds at systemic velocity with the 21 cm 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 ±200 km s-1 at several locations along the path of the jet. The HeIλ2.058 μm line in NGC 4151 appears in emission with a blueshifted absorption component from an outflow. The emission (absorption) component has a velocity offset of 10 km s-1 (−280 km s-1) with a Gaussian (Lorentzian) full-width (half-width) at half maximum of 160 km s-1 (440 km s-1). 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 1 × 1014 cm-2 with a covering factor along the line-of-sight of Clos ≃ 0.1.
Key words: galaxies: active / galaxies: Seyfert / galaxies: individual: NGC 4151
Figures 20–24 and Appendices are available in electronic form at http://www.aanda.org
© ESO, 2013
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