Spectropolarimetery of the Ultraluminous Infrared Galaxy IRAS 110548–1131

Summary

Abstract

From spectropolarimetric observations of the galaxy, IRAS 110548-1131 we report strong, broad Hα emission (FWHM 7600 km s⁻¹) in the polarized flux spectrum. This suggests that IRAS 110548-1131 has an obscured broad line region, whose radiation is scattered into our-line-of-sight by scatterers outside the obscured region.

Introduction

Since the discovery by Antonucci & Miller (1985) and its confirmation by Bailey et al. (1988) that the type II Seyfert galaxy NGC 1068 has broad hydrogen Balmer lines in it's polarized flux spectrum, and therefore has a Seyfert I type nucleus, it has been possible to construct a physical model in which the two types of Seyfert are in fact the same. Whether an object is seen as a type I or II depends upon the orientation of the galaxy and obscuration of the broad line region, probably in the form of a dusty torus, although the universality of such a model is an open question. Radiation from the BLR can escape along the axis of the torus and then be scattered into the line-of-sight by electrons and/or dust. The scattered component of these lines should then be observable in polarized flux.

In recent years there has been considerable interest in those galaxies identified from the IRAS survey which are very luminous in the far infrared region. Some evidence that highly luminous IRAS galaxies contain obscured QSO nuclei comes from the work of Hough et al.