The Interpretation of the Emission Spectra of the Seyfert 2 Galaxy NGC 7130: Determination of the Active Galactic Nucleus and Starburst Contributions

Detailed modeling of the different regions of NGC 7130 is presented, accounting for its composite nature of an active galactic nucleus (AGN) and a starburst galaxy. Shock waves, created by stellar winds from hot massive stars and by supernova ejecta, are evident in the continuum and line spectra emitted from the clouds. Therefore, the SUMA code, which accounts consistently for photoionization and shocks, is adopted in model calculation. The results show that the nuclear region is dominated by gas ionized by a power-law radiation flux from the active center (AC). High-velocity (Vs = 1000 km s-1) clouds, which account for the broad FWHM component of the line profile, are found close to the AC and are characterized by a high dust-to-gas ratio (>10-12, while the dust-to-gas ratio is about 10-14 throughout the galaxy). Massive stars with temperatures of (5-7) × 104 K photoionize and heat the gas in the outer regions, and old star population (T* = 3000 K) background radiation contributes to the fit of the continuum in the optical-near-IR range. The AGN-starburst connection is discussed on the basis of model results, considering, particularly, the distribution of densities and velocities throughout the galaxy.