Nuclear obscuration and scattering in Seyfert 2 galaxies

¹ Department of Astronomy, Nanjing University, Nanjing 210093, PR China
² Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo Postal 70-264, Mexico DF 04510, Mexico
³ Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 5015 Firenze, Italy

Corresponding author: Q. Gu, qsgu@nju.edu.cn

Received: 19 October 2000
Accepted: 13 November 2000

Abstract

We study the relationship between gaseous absorbing column density (N_H), infrared colors and detectability of the broad lines in a large sample of Seyfert 2 galaxies(Sy2s). We confirm that Sy2s without polarized broad lines tend to have cooler 60 μm/25 μm colors; this correlation was previously ascribed to the effect of obscuration towards the nuclear region. We find some evidence that Sy2s without polarized broad lines have larger absorbing column density (N_H) and that a fraction of them are characterized by dust lanes crossing their nuclei. However, we find that the IR colors do not correlate with N_H, in disagreement with the obscuration scenario. Also, Sy2s without polarized broad lines follow the same radio-FIR relation as normal and starburst galaxies, at variance with Sy2s with polarized broad lines. These results indicate that the lack of broad lines in the polarized spectrum of Sy2s is mostly due to the contribution/dilution from the host galaxy or from a circumnuclear starburst, though a lesser extent to the obscuration toward the nuclear region also plays a role.