Star Formation in NGC4449: MAMA-Detector UV Imagery and Fabry-Perot Balmer-Line Imagery

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Session 31 -- Star-Forming Galaxies
Display presentation, Tuesday, 9:30-6:30, Heller Lounge Room

[31.08] Star Formation in NGC4449: MAMA-Detector UV Imagery and Fabry-Perot Balmer-Line Imagery

Andrew M. Smith (Laboratory for Astronomy and Solar Physics, NASA/GSFC), Robert S. Hill (Hughes STX Corp.), Allen J. Home, Fred C. Bruhweiler (CUA), K.-P. Cheng, Paul M. N. Hintzen, Ronald J. Oliversen (Laboratory for Astronomy and Solar Physics, NASA/GSFC)

NGC 4449 is a Magellanic irregular galaxy with vacuum ultraviolet (VUV) luminosity comparable to late-type spirals and greater than that of the LMC by $\sim 2.5$ mag, indicating substantial star formation in the last $10^8$ yr. Using VUV and Balmer-line images, we investigate the star formation history of 22 large OB complexes during this recent time interval. A group of VUV and H$\alpha$ sources in the north of the galaxy, associated with a particular H{\sc i} feature, is producing stars actively at the present time. By contrast, VUV sources along the northeast-southwest surface brightness ridgeline (the ``bar'') appear to be less active at the present, though star formation has clearly occurred in the last $10^7$ yr, and morphology suggestive of multigeneration star formation is seen. Over the entire galaxy, star formation rates are consistent on time scales of $10^6$, $10^8$, and $10^9$ yr, confirming the results of previous investigators. Red and blue continuum images show dust features in the neighborhood of the ridgeline with a filamentary morphology coherent over $\sim 100$ pc. Imagery in H$\alpha$ confirms the ionized-gas morphology found by previous investigators, including many compact knots, as well as radial filaments, loops, and ``froth'' filling the visible system. A partial oval of bright H{\sc ii} regions is found along the ridgeline, as are the most luminous VUV sources.

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