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P.L. Shopbell (UMD), B. Buckalew, R.J. Dufour (Rice U.), D.K. Walter (SCSU)
We present new HST/WFPC2 narrowband imagery of the nearby (D ~ 1.7~Mpc) dwarf irregular galaxy NGC~1569. The combination of this galaxy's proximity and the high spatial resolution of HST provides us with an unprecedented look at the complex ionized gas distribution prevalent in such low-mass starburst systems. Images taken at [OIII] 5007Å, H\alpha, and [SII] 6717Å+6731Å\ wavelengths allow for a detailed analysis of gas excitation processes. The morphology and distribution of the ionized gas are compared with standard empirical diagnostic diagrams to assess the importance of photoionizing sources with in-situ alternatives, i.e., shocks. In order to further investigate photoionization mechanisms, we have obtained imagery in the 4686Å\ line of HeII, a line strongly associated with Wolf-Rayet stellar populations. All imagery have been extinction-corrected in the standard fashion using an H\beta 4861Å\ image and the known Balmer decrement. These imagery are compared with published observations and dynamic models of dwarf irregular galaxies, with the aim of better understanding the interactions between star formation and evolutionary processes and the ambient ISM of the galaxy.
Support for this work was provided by NASA through grant number GO-08133.01-97A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.