FORMATION OF RAMAN SCATTERING WINGS AROUND Hα, Hβ, AND PAα IN ACTIVE GALACTIC NUCLEI

Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far-UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines, which can be identified with broad wings. We produce H alpha, H beta, and Pa alpha wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density N-H (I) being roughly proportional to N-H I(1/2). In particular, with N-H (I) = 10(23) cm(-2) the H alpha wings typically show a width similar to 2 x 10(4) kms(-1). We also find that H alpha and Paa wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for H beta wings.