I am currently studying galaxies which have low ionization nuclear emission line regions (LINERs) and other nearby galaxies that show nuclear activity, such as low luminosity active galactic nuclei (LLAGNs), starburst galaxies, and H II/LINER "transition" objects. My primary objective is to determine the ionization mechanisms in these nuclei and to find any links that exist between the different classes of objects. For example, there is mounting evidence that some LINERs are the small scale extension of the AGN phenomenon, ie., compact accreting objects which photoionize surrounding gas. On the other hand, line ratio diagrams are populated quite smoothly by objects ranging from H II region type spectra to LINER type spectra, suggesting a common link. Furthermore, the UV spectra of some of these nuclei are clearly dominated by young, hot stars. Another possible excitation mechanism is shock heating. Certain shock models have been shown to match some of the observed features of LINERs.

    Specifically, I am analyzing multiwavelength data and using photoionization modeling (with CLOUDY) to test the possible ionization mechanisms in these objects. In a recent study, we have shown that NGC 1052 (see figure below), often considered to be the "protypical" LINER galaxy, can be modeled successfully as a bona fide AGN. A preprint of this article can be found at astro-ph/0001346. These results are scheduled to appear in the Astrophysical Journal. Additionally, for nuclei with observable features due to a young stellar population, such as NGC 4569 (a galaxy which I am currently working on), I have used population synthesis modeling to determine the intrinsic ionizing spectral energy distribution.

    I wish to incorporate these results on individual galaxies into the broader picture, namely, to determine the basic physical nature of these various classes of nearby active galaxies. In order to accomplish this, I am combining my results with various surveys of nearby galaxies at different wavelengths.
 

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