AN ULTRAVIOLET AND NEAR-INFRARED VIEW OF NGC-4214 - A STARBURSTING CORE EMBEDDED IN A LOW SURFACE BRIGHTNESS DISK

During the Astro-a Spacelab mission in 1995 March, the Ultraviolet Ima ging Telescope (UIT) obtained far-UV (lambda = 1500 Angstrom) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial res olution of similar to 3 '' and a limiting surface brightness, mu(1500) > 25 mag arcsec(-2), permitting detailed investigation of the intensi ty 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 reve als the presence of a starbursting core embedded in an extensive low s urface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r less than or similar to 2.5 kpc) with similar to 15 resolved sources embed ded in bright, diffuse emission; and a population of fainter knots ext ending to the edge of the optically defined disk (r approximate to 5 k pc). The FUV light, which traces recent massive star formation, is obs erved to be more centrally concentrated than the I-band light, which t races the global stellar population The FUV radial light profile is re markably well represented by an R-1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the resu lt of an interaction, possibly a tidal encounter, with a dwarf compani on(s). The brightest FUV source produces similar to 8% of the global F UV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of t he FUV light distribution, giving NGC 4214 an active galactic nucleus- like morphology. Another strong source is present in the I band, locat ed 19 '' west, 10 '' north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucl eus of NGC 4214 or an evolved star cluster with an age greater than si milar to 200 Myr. The global star formation rate derived from the tota l FUV flux is consistent with rates derived using data at other wavele ngths and lends support to the scenario of roughly constant star forma tion during the last few hundred million years at a level significantl y enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasi zes the danger of classifying galaxies based on their high surface bri ghtness components at any particular wavelength.