NICMOS imaging of molecular hydrogen emission in seyfert galaxies

We present near-infrared (NICMOS) imaging of broadband and molecular hydrogen emission in Seyfert galaxies. In six of 10 Seyfert galaxies we detect resolved or extended emission in the 1-0 S(1) 2.121 μm or 1-0 S(3) 1.9570 μm molecular hydrogen lines. We did not detect emission in the most distant galaxy or in two Seyfert 1 galaxies because of the luminosity of the nuclear point sources. In NGC 5643, NGC 2110, and Mrk 1066, molecular hydrogen emission is detected in the extended narrow-line region on scales of a few hundred parsecs from the nucleus. Emission is coincident with [O III] and Hα + [N II] line emission. This emission is also near dust lanes observed in the visible to near-infrared color maps, suggesting that a multiphase medium exists near the ionization cones and that the morphology of the line emission is dependent on the density of the ambient media. The high 1-0 S(1) or S(3) H₂ to Hα flux ratio suggests that shock excitation of molecular hydrogen (rather than UV fluorescence) is the dominant excitation process in these extended features. In NGC 2992 and NGC 3227 the molecular hydrogen emission is from 800 and 100 pc diameter "disks" (respectively) that are not directly associated with [O III] emission and are near high levels of extinction (Av ≳ 10). The molecular hydrogen emission in NGC 4945 appears to be from the edge of a 100 pc superbubble. The molecular gas in these three galaxies could be excited by processes associated with local star formation. We confirm previous spectroscopic studies finding that no single mechanism is likely to be responsible for the molecular hydrogen excitation in Seyfert galaxies.