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Session 10 - Spiral Galaxies.
Display session, Monday, June 10
Great Hall,
During the Astro-2 Spacelab mission in March 1995, the Ultraviolet Imaging Telescope obtained far-UV (\lambda\lambda\ 1500 Åimagery of \sim 35 galaxies exhibiting recent massive star formation. The sample includes large disk systems, irregular, dwarf, and blue compact galaxies. These images have a spatial resolution of \sim 3\arcsec and a limiting surface brightness, \mu_1500 \approx 24.5 mags arcsec^-1.
The objects span an observed FUV luminosity range from -17 to -22 mags. We derive global star formation rates by comparing the observed FUV fluxes to the predictions of stellar population models. The UV-derived astration rates are compared to those derived from H\alpha and thermal infrared fluxes to explore the utility of star formation rates estimated from FUV data, and the star formation histories of these systems.
The ratio of FIR to FUV astration rates is a measure of the ``buried'' massive star component. The FUV to H\alpha ratio is sensitive to the relative strength of the most recent massive star formation, (t \alt 10 Myr), to that over typical dynamical timescales (t \alt 200 Myr). In several systems the FIR/FUV astration rate ratio is \sim 2-4, indicating that essentially all of the massive star formation is visible. This suggests that the FUV photometry, with modest extinction corrections, can provide reliable star formation estimates. Even in some dusty, IR-luminous systems, where the estimated FUV/FIR star formation ratio is \agt 10, we observe substantial FUV luminosity.
