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We present observations and analysis of the central region of the spiral galaxy M100 based on images taken with the Ultraviolet Imaging Telescope (UIT), ground-based CCD images, and archival IUE and ground-based spectra.
The UIT data, taken in the near UV (UIT filter A5, centered at 2560 A) and in the far UV (UIT filter B5, centered at 1620 A), show the UV nucleus to be a crescent shaped region containing two principal bright components. One component, located 6" (400 pc) due north of the geometric center, is roughly circular with a diameter of 7" and contributes approximately 8 percent of the total far UV flux from the nucleus. The other component is an arc shaped region located to the west and south with dimensions 6" wide and 20" (1.4 kpc) long and contributes approximately 25 percent of the far UV nuclear flux. We present radial surface brightness profiles in the UV and compare with similar ones from the galaxies M74, M81 and M33.
We obtained U, B, V, R, and H-alpha ground-based CCD images of M100. The central 3 arcseconds is relatively bright in the optical continuum and H-alpha, but appears as a local minimum in the UV. Differences between optical continuum, H-alpha, and UV morphology are used to map star formation and gas distribution. We also use a combination of published ground-based spectra, UIT photometry, and archival IUE spectra to synthesize the stellar population and to determine the star formation rates within the nuclear region.
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