Sep 06, 2018 4:00 pm - Nielsen Hall 170 - Colloquium
Aida Wofford - IA-UNAM (Ensenada)
Stars and gas in the most metal-poor galaxies: SBS 0335-052E

Improving our understanding of star formation at low metallicity is of large relevance for a variety of fields in astrophysics since it relates to multiple topical questions. These range from understanding the properties of galaxies that contributed to cosmic reionization to the evolution of metal poor massive stars that give rise to the formation of heavy binary black holes. Crucial are observational constraints for the theoretical predictions, which can be obtained from rest-frame UV and optical spectra of local star-forming dwarf galaxies with ionized-gas oxygen abundances at the low-metallicity  threshold of the nearby Universe. Only two such galaxies have coverage from H I Lyman-alpha (1216 Ang) to C III] 1909 Ang at a spectral resolution which is sufficient for disentangling stellar, nebular, and foreground spectral features in the UV: I Zw 18 and SBS 0335-052E. These are two of the nearest most metal-poor galaxies known in the Universe. We recently used the Hubble Space Telescope / Cosmic Origins Spectrograph and Very Large Telescope / Multi Unit Spectroscopic Explorer to obtain rest-frame UV and optical spectroscopy of SBS 0335-052E. The data have  spectral resolutions of FWHM˜20 km/s and FWHM˜150 km/s, respectively. We use these high-quality data to test model spectra of the integrated light of stars + gas + dust, which includes very massive  stars of up to 300 Msun. We use Bayesian inference techniques to derive physical properties of the gas and stars in the galaxy. Our study provides a first quantitative estimate of the accuracies and uncertainties of the most recent spectral synthesis models of young stellar populations and demonstrates the good progress of models in fitting high-quality observations.