Modeling the Continuum and Line Spectra of the Seyfert 2 Galaxy NGC 5252

Abstract

The S0 galaxy NGC 5252 is one of the best examples of the anisotropic radiation theories believed to govern the physics of active galactic nuclei. Considerable amounts of observational data, from the radio to the hard X-ray domain, have been accumulated from the central nuclear region of this galaxy. This work makes use of all the available observational information in an attempt to model in a self-consistent manner the continuum and line emission spectra of the nuclear region and the extended emission-line region. It is suggested that both the nuclear continuum and the nuclear line emission originate in gaseous clouds that are exposed to the nuclear ionizing radiation and subjected to shocks. The best fit to the data in the nuclear region is obtained with a weighted-average model that includes radiation-dominated clouds with low velocities (100 km s-1), producing most of the emission lines and the low-frequency continuum, and high-velocity (~400 km s-1) shock-dominated clouds, where the soft X-ray continuum originates. The far-infrared emission is due to dust heated by both the nuclear radiation and shocks. Modeling of the extended emission-line region was performed on the basis of the derived nuclear model. That region was found to be characterized by densities of a few cm-3 and a cloud size of about 100 pc. Excitation via shocks is found negligible, whereas photoionization by the central power source widely accounts for the observed line spectrum.