Spectral synthesis in the ultraviolet. II - Stellar populations and star formation in blue compact galaxies

Abstract

Far-UV spectra of seven blue compact galaxies have been obtained with the IUE satellite. These objects span a range in luminosity of -21 ≤ MB ≤ -13. The authors have investigated their stellar content and star formation history by applying the technique of optimizing population synthesis utilizing their library of far-UV stellar spectra. The far-UV absorption-line spectra of these galaxies are clearly composite, with the signatures of main-sequence types between O3 and mid-A. Good fits to the data are obtained with the synthesis technique. The solutions yield stellar luminosity functions which display large discontinuities, indicative of discrete star formation episodes or bursts. Continuous star formation cannot account for the observations. Star formation rates can be estimated for the hot stars detected directly in the UV. In the more luminous galaxies Haro 1 and Haro 15, ≡3 M_sun;yr-1 of gas is being converted into massive stars, a value independent of the nature of the initial mass function.