Evolutionary synthesis models are used to constrain the star formation
history from the absolute ultraviolet flux and from the stellar components of
the absorption lines SiIV and CIV, and from the far ultraviolet lines
OVI+L
+CII. The
spectral energy distributions from these models are used as input to the
photoionization code CLOUDY to predict [OIII]/H and the column densities of the cool component
of the ionized gas (SiII and CII) associated with the HII region. The results
indicate continuous star formation during about 9 Myr or, alternatively,
bursts with an age between 3 and 6 Myr, and a mass consistent with that from
the H
flux. Evidence for significant
dilution by a field star population is found in all galaxies, except
NGC 6090.
Most of the interstellar absorption lines are saturated. Their equivalent widths indicate a large velocity dispersion in the gas. Other evidence for large scale-motions of the interstellar gas comes from blueshifts of several hundred km s-1 with respect to the systemic velocity in the interstellar lines of NGC 6090, Mrk 66, and IRAS 0833+6517. These outflows are most likely driven by the starburst.
L was detected in emission in three
of the galaxies (NGC 6090, Mrk 66, and IRAS 0833+6517). The
dereddened ratio L/H in IRAS 0833+6517 is
close to the recombination value, indicating that extinction is more important
than multiple resonant scattering effects. However, the GHRS spectrum of
IRAS 0833+6517 clearly shows that the emision profile of
L is asymmetric, with the blue
wing being absorbed by neutral gas. This indicates that the velocity
structure of the neutral gas and the scattering by HI atoms can
play an important role in the escape of the
L photons as well.