A multi-wavelength study of the nature of type 1.8/1.9 Seyfert galaxies.
TRIPPE M.L., CRENSHAW D.M., DEO R.P., DIETRICH M., KRAEMER S.B., RAFTER S.E. and TURNER T.J.
Abstract (from CDS):
We focus on determining the underlying physical cause of a Seyfert galaxy's appearance as type 1.8 or 1.9. Are these "intermediate" Seyfert types typical Seyfert 1 nuclei with reddened broad-line regions? Or are they objects with intrinsically weak continua and broad emission lines? We compare measurements of the optical reddening of the narrow and broad-line regions with each other and with the X-ray column derived from XMM-Newton 0.5-10 keV spectra to determine the presence and location of dust in the line of sight. We also searched the literature to see if the objects showed evidence for broad-line variability, and determined if the changes were consistent with a change in reddening or a change in the intrinsic ionizing continuum flux. We find that 10 of 19 objects previously classified as Seyfert 1.8/1.9s received this designation due to their low continuum flux. In four objects, the classification was due to broad emission-line region reddening, either by the torus or dust structures in the vicinity of the narrow emission-line region; in the remaining five objects there is not sufficient evidence to favor one scenario over the other. These findings imply that, in general, samples of 1.8/1.9s are not suitable for use in studies of gas and dust in the central torus.