Hubble Space Telescope Observations of Star-forming Regions in NGC 3994/3995

We obtained ultraviolet and optical images of star-forming regions in the interacting galaxy system NGC 3994/3995 using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We describe the characteristics of 56 detected knots, a majority of which are younger than 20 Myr old. There is no discernible pattern of knot age with respect to position within the galaxies. The knots have masses and radii ranging from 7.2×10³ to 4.4×10⁶ M_solar and from 4 to 23 pc, respectively. Using a conservative criterion, we find that ~15% of these knots may be proto-globular clusters; the percentage of proto-globular clusters may be as high as ~70%. The UV flux distribution of the knots in NGC 3995 can be fitted with a power law with α=-0.72+/-0.11, with no turnover detected brightward of the completeness limit.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.