Bibcode
Reunanen, J.; Kotilainen, J. K.; Prieto, M. A.
Bibliographical reference
Monthly Notice of the Royal Astronomical Society, Volume 343, Issue 1, pp. 192-208.
Advertised on:
7
2003
Citations
69
Refereed citations
62
Description
We present subarcsec near-infrared 1.5-2.5 μm 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, and are used to study the spatial extent of the
line emission, the integrated masses of excited H2 and the
excitation mechanisms of interstellar gas.
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 per cent) galaxies, in agreement with the unified
models of active galactic nuclei. The full width at half maximum (FWHM)
sizes of the nuclear H2 emission range from <20 to ~300
pc, and are larger than the predicted sizes for molecular torus (1-100
pc). Thus the emission probably arises from the material surrounding the
torus rather than directly from the torus.
Broad Brγ was detected in nearly half of the optically classified
Seyfert 2 galaxies, including two objects with no evidence for a hidden
polarized broad line region. This high detection rate stresses the
importance of extinction effects as the main cause for the Seyfert
dichotomy.
Brγ and [Fe II] correlate both spatially and kinematically.
Nuclear [Fe II] emission is generally blueshifted which, together with
the high Brγ/[Fe II] ratios, suggests shocks as the dominant
excitation mechanism in Seyfert galaxies.
Bright coronal emission lines [SiVI] and [Si VII] are common in
Seyferts, as they are detected in ~60 per cent of the galaxies. In three
galaxies the coronal lines are extended only in the direction parallel
to the cone. This could be explained by a strongly collimated radiation
field or, most plausibly, by shock excitation due to the jet or
superwind interacting with the interstellar medium.