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Star formation in NGC 4449: MAMA-detector UV imagery and Fabry-Perot Balmer-line imagery
Hill, Robert S.; Home, Allen T.; Smith, Andrew M.; Bruhweiler, Fred C.; Cheng, K. P.; Hintzen, Paul M. N.; Oliversen, Ronald J.
AA(NASA. Goddard Flight Center, Greenbelt, MD, US), AB(NASA. Goddard Flight Center, Greenbelt, MD, US), AC(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AD(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AE(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AF(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AG(NASA. Goddard Space Flight Center, Greenbelt, MD, US)
The Astrophysical Journal, vol. 430, no. 2, pt. 1, p. 568-580 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Balmer Series, Galactic Clusters, Galactic Evolution, Irregular Galaxies, Luminosity, Star Formation, Ultraviolet Spectroscopy, Astronomical Models, Cosmology, Fabry-Perot Interferometers, Multi-Anode Microchannel Arrays, Spectrum Analysis, Ultraviolet Astronomy, Ultraviolet Photometry
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Using far-ultraviolet (FUV) and Balmer-line imagery, we investigate the star formation history of 22 large OB complexes in the Magellanic irregular galaxy NGC 4449. The FUV luminosity of NGC 4449 is comparable to those of late-type spirals and is greater than that of the LMC by approximately 2.4 mag, indicating substantial star formation in the last 108 yr. FUV data were taken using a sounding-rocket telescope with a Multianode Microchannel Array (MAMA) detector, and Balmer-line data were taken using the Goddard Fabry-Perot Imager. The resulting imagery shows bright, roughly coincident FUV and H alpha sources throughout the extent of the visible galaxy. We model these sources using cluster-evolution codes. Although all sources are a few Myr old, clear age differences are found. In particular, several of the most recently active star formation regions are located together in the galaxy's northern periphery, which is apparently coincident with a large H I reservoir. The brightest and most massive OB complexes are found along the northeast-southwest surface brightness ridgeline (the 'bar'). Over the entire galaxy, star formation rates are consistent on timescales of 106, 108, and 109 yr. A history of recent star formation is suggested with two main episodes, one predominantly in the bar ending approximately 5 Myr ago, and an ongoing one associated with an observed H I cloud.

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