Starbursts in galaxies

Clusters of massive stars are born in `Starbursts' when galaxies collide, as seen in the Antennae galaxies. In an Infrared Space Observatory (ISO) programme I have used mid-IR spectra of WR galaxies to determine their physical and chemical properties and the nature of their massive star populations. We have also provided a recent update -- Starburst02 to the Starburst99 population synthesis code, to take into account metallicity dependent line blanketed model atmospheres for O and WR stars. We have also used ESO telescopes to study the massive stellar content of starburst clusters in NGC 3125 (see HST/ACS figure), for which we have resolved previous UV and optical results through use of common interstellar extinction law.


Finally, we are also investigating the chemical properties of high-redshift Lyman break galaxies, such as MS1512-cB58 and Q1307-BM1163, sampling an epoch when the universe was only a few Gyr old, using the stellar wind signatures from massive OB stars in their integrated spectra. Surprisingly, the metal content of such early galaxies as indicated by oxygen, is already within a factor of a few of the present Milky Way galaxy.