Astronomy and Astrophysics – Astronomy
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...481..735f&link_type=abstract
Astrophysical Journal v.481, p.735
Astronomy and Astrophysics
Astronomy
15
Ultraviolet: Galaxies, Galaxies: Irregular, Galaxies: Individual Ngc Number: Ngc 4214, Infrared: Galaxies
Scientific paper
During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV ( lambda = 1500 Angstroms) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3" and a limiting surface brightness, mu 1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r <~ 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r ~ 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus--like morphology. Another strong source is present in the I band, located 19" west, 10" north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other wavelengths and lends support to the scenario of roughly constant star formation during the last few hundred million years at a level significantly enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasizes the danger of classifying galaxies based on their high surface brightness components at any particular wavelength.
Bohlin Ralph
Fanelli Michael N.
Freedman Wendy L.
Madore Barry
Neff Susan G.
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