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Abstract

In this thesis I study the gas distribution and dynamics, as well as the stellar populations, in the circumnuclear star forming rings in the nearby barred galaxies NGC5248 and NGC6951. Circumnuclear star forming rings are regions of high gas and star formation density in the centers of disk galaxies. These star formation rings can have a strong influence on the secular evolution of their host galaxies, by halting gas inflow towards the nucleus. The gas masses that build up in these rings are high and this consequently leads to intense star formation. This makes circumnuclear star forming rings also an important tool to build up the stellar (pseudo-)bulge. These two galaxies were selected because they have very similar global properties (mass, size, metallicity), but very different circumnuclear regions, both of which containing circumnuclear star forming rings. Detailed investigation of both, and a comparison between them, thus provides new detailed insight on the interplay between circumnuclear star forming rings and the circumnuclear region as a whole. Three questions are addressed in this work. First of all, I investigate the true effectiveness of the circumnuclear rings as a gas barrier in both galaxies. I study star formation progression in these rings and its relation to the gas flow onto the ring. The age and life span of the circumnuclear rings is derived from the analysis of their stellar populations. In both galaxies I find that while the circumnuclear rings are effective barriers, they are not absolute ones. The interplay between the large scale stellar bar, circumnuclear ring and other dynamical components in the circumnuclear region allows some gas to flow towards the very center past the ring. I find that the location of the youngest stars in the ring is close to the inflow position of the gas onto the ring in both galaxies, consistent with star formation proceeding in a ’pearls-on-a-string’ mechanism with the youngest ’pearls’ close to the gas inflow location. Finally, I derive ages of the rings around 1.5 Gyr, which implies that circumnuclear star forming rings have a significant amount of time to shape the circumnuclear regions of their host galaxies.