Long-Term Variability in the Optical Spectrum of the Seyfert Galaxy NGC 2992

TL;DR

This study observes long-term optical spectral variability in NGC 2992, revealing a change from Seyfert 1.9 to Seyfert 2, likely due to intrinsic continuum changes rather than obscuration, challenging traditional AGN unification models.

Contribution

It provides new spectral data showing that Seyfert type changes in NGC 2992 are driven by continuum variability, not just dust obscuration, offering insights into AGN classification dynamics.

Findings

NGC 2992 changed from Seyfert 1.9 to Seyfert 2 in 2006

Variations are likely due to intrinsic continuum changes, not dust obscuration

Different regions near the nucleus show similar absorption properties

Abstract

New spectra of NGC 2992 from the Cerro Tololo Inter-American Observatory show that this nearby AGN has 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 Halpha 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.