A Multi-wavelength Study of the Nature of Type 1.8/1.9 Seyfert Galaxies

• Published in: The Astrophysical journal Vol. 725; no. 2; pp. 1749 - 1767
• Main Authors: Trippe, M. L, Crenshaw, D. M, Deo, R. P, Dietrich, M, Kraemer, S. B, Rafter, S. E, Turner, T. J
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 20-12-2010; IOP
• Subjects: Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC RAY SOURCES; COSMIC X-RAY SOURCES; DUSTS; Earth, ocean, space; EMISSION; Exact sciences and technology; GALAXIES; SEYFERT GALAXIES; WAVELENGTHS; X-RAY GALAXIES; galaxies: Seyfert; infrared: galaxies; X-ray galaxies; Variability; X-rays: galaxies; Cosmic x-ray sources; Continuum; Active galaxies; Seyfert galaxies; Narrow line region; Tori; galaxies: active; Classification; Infrared galaxies; Broad line region; Emission line
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/725/2/1749

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.