| In this dissertation, a detailed study of the ionization mechanism of two LINER galaxies, NGC 1052 and NGC 4569, is presented. The HST/WFPC2 imagery of NGC 1052 clearly differentiates extended nebular Hα emission from that of the compact core. The observed strengths of the Balmer emission lines derived from the HST/FOS spectrum indicates substantial intrinsic reddening of the nuclear nebular emission, E(B-V) = 0.42. This is the first finding of a large extinction in NGC 1052. If the central ionizing continuum is assumed to be attenuated by a comparable amount, then the emission line spectrum can be reproduced well by a simple photoionization model. This model assumes a central power-law continuum source, Fν ∝ ν α, with a spectral index of α = −1.2, as deduced from the UV and X-ray data. A multi-density, dusty gas gives the best fit to the observed emission line spectrum. Calculations show that photoionization by the derived continuum can also reproduce the small contribution from a highly ionized region that is observed in NGC 1052. In NGC 4569, spectral synthesis analysis indicates that the nuclear UV emission is from a massive, compact starburst that is 5–6 Myrs old. An observationally derived constraint is placed on the possible contribution from hot Wolf-Rayet stars. Photoionization analysis indicates that the emission line spectrum of NGC 4569 can be driven solely by stellar photoionization, however, a distinct geometry of the emission line gas is required. This may be a product of the strong stellar winds and supernovae associated with the young stellar population. |
