NICMOS imaging of molecular hydrogen emission in Seyfert galaxies

We present near-infrared (NICMOS) imaging of broadband and molecular hydrog en emission in Seyfert galaxies. In six of 10 Seyfert galaxies we detect re solved or extended emission in the 1-0 S(1) 2.121 mu m or 1-0 S(3) 1.9570 m u m molecular hydrogen lines. We did not detect emission in the most distan t galaxy or in two Seyfert 1 galaxies because of the luminosity of the nucl ear 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 H alpha + [N II] line emission. This emission is also near dust lanes observ ed in the visible to near-infrared color maps, suggesting that a multiphase medium exists near the ionization cones and that the morphology of the lin e emission is dependent on the density of the ambient media. The high 1-0 S (1) or S(3) H-2 to H alpha flux ratio suggests that shock excitation of mol ecular hydrogen (rather than UV fluorescence) is the dominant excitation pr ocess in these extended features. In NGC 2992 and NGC 3227 the molecular hy drogen 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 (A(V) greater than or similar to 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 ass ociated with local star formation. We confirm previous spectroscopic studie s finding that no single mechanism is likely to be responsible for the mole cular hydrogen excitation in Seyfert galaxies.