Starburst regions in external galaxies and the link to active galactic nuclei

Starburst galaxies show pronounced star formation rates and high luminosities. The underlying processes involved with these intense bursts of star formation, as well as of the subsequent evolution of stars formed during these bursts, are not yet fully understood. A thorough understanding of these processes is essential to an understanding of the fundamental astrophysical processes involved in stellar and galactic evolution.; Evolutionary synthesis routines are commonly used to generate synthetic flux distributions of starburst regions, and thereby yield estimates of such variables as cluster age, star formation rate, and distribution of stellar mass and type. Such routines can be enhanced by an additional input parameter, namely, heavy element abundance (metallicity). A metallicity parameter can render synthetic flux distributions more applicable to starburst galaxies, which can be significantly deficient in heavy elements. The metallicity of a starburst cluster can greatly affect stellar features, and must therefore be considered when analyzing starburst spectra.; To incorporate a metallicity parameter in an existing evolutionary synthesis routine, stellar libraries from the metal-deficient, Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) have been generated. The flux distributions of selected stars from these galaxies can be accessed by the evolutionary synthesis routine. The routine selects and integrates stellar fluxes to generate synthetic starburst flux distributions.; The SMC and LMC stellar libraries are constructed from archival International Ultraviolet Explorer spectra. To ensure consistency of the stellar classifications, ultraviolet classification systems, applicable to galaxies of metallicities comparable to the SMC and LMC, are developed. These UV classification systems and the spectral diagnostics developed in conjunction with the systems will be useful for future datasets from such collection systems as the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope.; Finally, the enhanced evolutionary synthesis routine is applied to four starburst galaxies. Such parameters as cluster age, metallicity, and distribution of stellar mass and type are determined for each of these starburst regions. Differences from conclusions drawn in previous analysis attempts are highlighted, and the importance of the newly added metallicity parameter is underscored. The possible evolutionary link between starbursts and AGNs, as supported by these results, is discussed.