Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular content and coronal emission

Abstract

We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to the ionization cone and perpendicular to it. These spectra complement similar data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large concentrations of molecular gas (H2) are present in the nucleus regardless of the Seyfert type. The spatial extent of the H2 emission is larger perpendicular to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly half of the optically classified Seyfert 2 galaxies, including two objects with no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is generally blueshifted which together with high BrGamma/[FeII] ratios suggests shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected in ~60 % of the galaxies. In three galaxies the coronal lines are extended only in the direction parallel to the cone. This could be explained by shock excitation due to the jet or superwind interacting with the interstellar medium.