The optical/near-infrared broad-line emission and hard X-ray continuum of active galactic nuclei and ultraluminous infrared galaxies

We compare the luminosities of the hard X-ray and optical/near-infrared broad-line emission from active galactic nuclei (AGNs) and ultraluminous infrared galaxies (ULIRGs). Both types of emission are thought to be good indicators of activity driven by supermassive black holes. We selected objects for which both X-ray and broad-line data are available, and, additionally, for which we can obtain information about the far-infrared and/or morphological properties. We find that, although the hard X-ray to broad Hat luminosity ratio L-X/L-(broad H alpha) is relatively constant in nearly all of the objects examined, there exist some objects showing a distinctly small L-X/L-(broad H alpha) ratio. These small L-X/L-(broad H alpha) objects are thought to be undergoing a merger based on 60 mu m-to-optical flux ratio and/or double nuclei morphology. This result could give us important information about the issue of the energy source of merging ULIRGs.