Starbursts
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.
The nearest starburst-like region is the Tarantula Nebula in the Large Magellanic Cloud which has been studied in detail via the VFTS survey, and revealed to possess an excess of massive stars. We have also use VLT-MUSE and HST to obtain the empirical UV and optical properties of the central NGC2070 region of the Tarantula, in order to test population synthesis codes.
We have also provided an update 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.
UV spectroscopy of very young super star clusters permits the identification of very massive stars, such as cluster 5 in NGC5253 (Smith et al. 2016). High resolution imaging of nearby star-forming galaxies has been obtained in the HST UV Legacy survey GULP.
Finally, we have also investigated the chemical properties of high-redshift (z~3) 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. JWST enables the Lyman break technique to identify extremely high redshift (z>10) star forming galaxies.
More information
On the reliability of CIV 1550 as an abundance indicator for high-redshift star forming galaxies, Crowther et al. 2006.
How extreme are the Wolf-Rayet clusters in NGC3125?, Hadfield and Crowther 2006.
The massive star population in the giant HII region Tol89 in NGC5398, Sidoli, Smith & Crowther 2006
An excess of massive stars in the local 30 Doradus starburst. Schneider et al. 2018
The Very Massive Star Content of the Nuclear Star Clusters in NGC5253 Smith et al. 2016
Mapping the core of the Tarantula Nebula with VLT-MUSE. III. A template for metal-poor starburst regions in the visual and far-ultraviolet. Crowther & Castro 2024