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D. Weistrop, D Eggers, A Stone, C.H. Nelson, R. Bachilla (UNLV)
NGC 3991, NGC 3994, and NGC 3995 comprise a small group of interacting galaxies. Groundbased images indicate significantly distorted morphology in NGC 3991 and NGC 3995, while NGC 3994 appears to be a normal, inclined spiral. Spectra of NGC 3991 and NGC 3995 have features typical of strong HII regions. NGC 3994 is a LINER. All three galaxies have strong ultraviolet emission and have been observed with IUE (Kinney, et al. 1993).
As part of an investigation of star formation in interacting galaxies, we have obtained ultraviolet and visible images of the central regions of NGC 3994 and 3995 with the Space Telescope Imaging Spectrograph on HST. Imaging was obtained in two ultraviolet (FUV-MAMA+F25QTZ, NUV-MAMA+F25CN182) and one visible (CCD+F28X50LP) band. Individual star forming knots (at HST resolution) have been identified in both galaxies.
In NGC 3994 star-forming knots are found tracing the spiral arms. Results from ground based spectroscopy indicate nuclear reddening of E(B-V) ~ 0.3- 0.4, suggesting that the lack of UV-bright knots in the center is real and not due to extinction. The knots in NGC 3995 have a distorted, 'hook shaped' distribution. The knots are typically 12 - 45 pc in diameter (FWHM), with observed FUV fluxes of approximately 10-17 to 10-16 ergs cm-2sec-1 Å-1.
We compare our imaging and spectroscopy data to current starburst models to constrain knot ages and masses. Knot characteristics as a function of location in the galaxy will also be discussed.
This work has been supported in part by NASA, under contract NAS5-31231, and through the Nevada Space Grant Consortium.