Long-term variability in the optical spectrum of the Seyfert galaxy NGC 2992.
TRIPPE M.L., CRENSHAW D.M., DEO R. and DIETRICH M.
Abstract (from CDS):
New spectra of NGC 2992 from the Cerro Tololo Inter-American Observatory show that this nearby active galactic nucleus changed its type classification to a Seyfert 2 in 2006. It was originally classified as a Seyfert 1.9, and has been previously seen as a Seyfert 1.5 with strong broad Hα emission. A comparison of the reddening and equivalent hydrogen column density derived for the narrow-line region from these new data with those previously calculated for different regions closer to the nucleus shows them to be very similar, and suggests that these different regions are all being absorbed by the same opacity source, a large 100 pc scale dust lane running across the nucleus. However, obscuration by dust in this lane is probably not responsible for classification changes which occur in only a few years. It is more likely that NGC 2992's observed variations are due to a highly variable ionizing continuum. We therefore conclude that, although NGC 2992 was originally identified as a Seyfert 1.9, this was not because of an oblique viewing angle through the atmosphere of a central dusty torus, but because its active nucleus was identified when it was in a low-continuum state.
galaxies: individual: NGC 2992 - galaxies: Seyfert