Physical Properties of Young Stellar Populations in 24 Starburst Galaxies Observed with FUSE

Abstract

We presents the main physical properties of very young stellar populations seen with FUSE in 24 individual starbursts. These characteristics have been obtained using the evolutionary spectral synthesis technique in the far-ultraviolet range with the LavalSB code. For each starburst, quantitative values for age, metallicity, initial mass function slope, stellar mass, and internal extinction have been obtained and discussed in details. Limits of the code have been tested. One main conclusion is that most starbursts (and probably all of them) cannot be represented by any continuous star formation burst in the far-ultraviolet. Also, quantitative values of various optical diagnostics related to these stellar populations have been predicted. Underlying stellar populations, dominated by B-type stars, have been detected in NGC 1140, NGC 4449, and possibly NGC 3991. We characterized the young stellar populations of less than 5 Myr in Seyfert 2 nuclei.