Star-forming Knots in the UV-bright Interacting Galaxies NGC 3395 and NGC 3396*

摘要

We have obtained ultraviolet and visible wavelength images for the central regions of the interacting galaxies NGC 3395 and NGC 3396, using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The images show many isolated sources of ultraviolet emission produced by young star-forming regions (knots). The FWHM of most of the knots in both galaxies is ≤20 pc. Far-UV flux distributions for the complete sample of knots can be fitted with a power law with exponent α = -1.20 ± 0.35 for NGC 3395 and a power law with exponent α = -0.69 ± 0.21 for NGC 3396. Comparison with models from Leitherer et al. indicates that the ages of most of the knots are ≤80 Myr. Reddening of the knots ranges from E(B-V) = 0.0 to E(B-V) = 0.3 mag, indicating variable amounts of dust in these regions. Almost all the knots have masses less than 106 M⊙. Many of the knots are probably bound and at least six knots are good proto–globular cluster candidates. There are no significant differences in the fluxes, sizes, and ages of the knots in the two galaxies. The average mass of the knots in NGC 3395 is an order of magnitude less than the average mass of the knots in NGC 3396. There is no obvious correlation between the age of a knot and its position the galaxy.