1998/08/06 by Robert S. Hill, Robert Hill, Michael N. Fanelli +12 · 1 citation
Physics and Astronomy · #Adaptive optics and wavefront sensing #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/306302
30 pages + 9 tables + 14 figs (GIF). Accepted for ApJ, 1 Nov 98, Vol 507, No. 1; until then, paper available as merged postscript file, ftp://abba.gsfc.nasa.gov/pub/bhill/pp/n4449_pp1.ps (figs better), tabs separate in same dir [2nd repl getting comment & landscape right]
arxiv created 1998/08/06 · openalex publication_date 1998/11/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
The bright Magellanic irregular galaxy NGC 4449 was observed during the Astro-2 Space Shuttle mission by the Ultraviolet Imaging Telescope (UIT), which obtained images of a 40' field centered on the galaxy in two broad far-ultraviolet (FUV) bands centered at 1520 and 1620 Å, with 3''-5'' spatial resolution. Together with Hα and Hβ fluxes from ground-based Fabry-Perot images, these data are analyzed in order to explore the recent star formation history of NGC 4449. Maps of the Hα-to-FUV and FUV-to-blue continuum flux ratios are presented and interpreted using evolutionary synthesis models. Photometry is presented both for 22 apertures containing large OB complexes and for 57 small apertures containing compact FUV-emitting knots. The OB complexes along the northern edge of the visible system have high Hα-to-FUV ratios and thus appear to be more dominated by the current generation of stars than are other parts of the galaxy. However, young sources do exist elsewhere and are particularly conspicuous along the bar. The small-aperture analysis shows three candidate regions for sequential star formation. Surface brightness profiles are consistent with an exponential disk in both the FUV and the optical continuum.