NICMOS Imaging of Molecular Hydrogen Emission in Seyfert Galaxies

We present NICMOS imaging of broad band and molecular hydrogen emission inSeyfert galaxies. In 6 of 10 Seyferts we detect resolved or extended emissionin the 1-0 S(1) 2.121 or 1-0 S(3) 1.9570 micron molecular hydrogen lines. Wedid not detect emission in the most distant galaxy or in the 2 Seyfert 1galaxies in our sample because of the luminosity of the nuclear point sources.In NGC 5643, NGC 2110 and MKN 1066, molecular hydrogen emission is detected inthe extended narrow line region on scales of a few hundred pc from the nucleus.Emission is coincident with [OIII] and H alpha+[NII] line emission. Thisemission is also near dust lanes observed in the visible to near-infrared colormaps suggesting that a multiphase medium exists near the ionization cones andthat the morphology of the line emission is dependent on the density of theambient media. The high 1-0 S(1) or S(3) H2 to H alpha flux ratio suggests thatshock excitation of molecular hydrogen (rather than UV fluorescence) is thedominant excitation process in these extended features. In NGC 2992 and NGC3227 the molecular hydrogen emission is from 800 and 100 pc diameter `disks'(respectively) which are not directly associated with [OIII] emission and arenear high levels of extinction (AV > 10). In NGC 4945 the molecular hydrogenemission appears to be from the edge of a 100 pc superbubble. In these 3galaxies the molecular gas could be excited by processes associated with localstar formation. We confirm previous spectroscopic studies finding that nosingle mechanism is likely to be responsible for the molecular hydrogenexcitation in Seyfert galaxies.Comment: submitted to Ap