Near-infrared long-slit spectra of Seyfert galaxies: gas excitation across the central kiloparsec^{⋆,⋆⋆,⋆⋆⋆}

¹ Institut de Radio, Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St-Martin d’Hères, Grenoble, France
e-mail: vanderlaan@iram.fr
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ European Space Agency, Keplerlaan 1, 2200AG Noordwijk, The Netherlands
⁴ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA

Received: 22 August 2013
Accepted: 11 October 2013

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.