  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. 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. 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.
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. The fully calibrated long-slit spectra, as well as our
fitting results, are made available on-line.
