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A number of galaxies have exhibited signs of extremely active star formation within their nuclei. Many of these galaxies show evidence for a non uniform distribution of dust that completely obscures the nucleus at visible wavelengths. Any quantitative model concerning the stellar luminosity function within these galaxies must accurately correct for this high and non uniform extinction. Many of these galaxies appear to have the same general geometry of neutral gas, ionized gas and stars within their central regions. This standard geometry consists of a hot central "cavity" consisting primarily of ionized gas and stars, surrounded by a foreground ring of molecular material that can be responsible for virtually all of the observed extinction. In this case, obtaining the extinction to the ionized gas can be used to determine the extinction to the stellar clusters, thereby allowing the analysis of the true luminosities and colors of these clusters. Although optical studies have traditionally been used to derive the extinction in galaxies, high resolution near-infrared recombination line observations can best probe the most obscured central regions.
We display high spatial ($\simeq 40$~pc) P$\beta$ (1.28~$\mu$m) and Br$\gamma$ images of M82 ($\lambda/\Delta\lambda\approx 800$) obtained with the National Air and Space Museum J/H-band Fabry-Perot and the Naval Research Lab K-band Fabry-Perot coupled to the Third Generation Rochester Infrared Camera at the Wyoming Infrared Observatory (WIRO). The implications of the derived extinction on the stellar mass function in the nucleus of M82 are discussed.
This work was supported in part by the Smithsonian Institution Scholarly Studies Program, NSF grant AST93-57392, and the Office of Naval Research. IR Astronomy at WIRO is supported by AST91-16644 (NSF).
