Near-infrared long-slit spectra of Seyfert galaxies: gas excitation across the central kiloparsec

Creators: van der Laan, T. P. R.; Schinnerer, E.; Böker, T.; Armus, L.

Abstract

Context. The excitation of the gas phase of the interstellar medium can be driven by various mechanisms. In galaxies with an active nucleus, such as Seyfert galaxies, both radiative and mechanical energy from the central black hole, or the stars in the disk surrounding it may play a role. Aims. We investigate the relative importance and range of influence of the active galactic nucleus for the excitation of ionized and molecular gas in the central kiloparsec of its host galaxy. Methods. We present H- and K-band long-slit spectra for a sample of 21 nearby (D < 70 Mpc) Seyfert galaxies obtained with the NIRSPEC instrument on the Keck telescope. For each galaxy, we fit the nebular line emission, stellar continua, and warm molecular gas as a function of distance from the nucleus. Results. Our analysis does not reveal a clear difference between the nucleus proper and off-nuclear environment in terms of excitation mechanisms, suggesting that the influence of an AGN reaches far into the disk of the host galaxy. The radial variations in emission line ratios indicate that, while local mechanisms do affect the gas excitation, they are often averaged out when measuring over extended regions.

Additional Information

© 2013 ESO. Article published by EDP Sciences. Received 22 August 2013. Accepted 11 October 2013. Published online 12 December 2013. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the anonymous referee for valuable comments that improved this paper. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We wish to thank Jesus Falcon-Barroso for help with the spectral fitting. Our thanks also go to Ariane Lançon for generating synthetic spectra from her models specifically at our spectral resolution. TvdL would like to acknowledge P. D. Barthel, who once upon a time wanted to see these data sets published and got her and ES talking. Part of this work was done during an 2011-2012 IPAC visiting graduate fellowship. The Digitized Sky Survey was produced at the Space Telescope Science Institute under US. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions.

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