Stellar Spectral Signatures in High-Redshift Galaxies

Stellar emission and absorption lines are routinely observed in galaxies at redshifts up to 5 with spectrographs on 8-10m class telescopes. While the overall spectra are well understood and have been successfully modeled using empirical and theoretical libraries, some challenges remain. Three issues are discussed: determining abundances using stellar and interstellar spectral lines, understanding the origin of the strong, stellar He II 1640 line, and gauging the influence of stellar Lyman-alpha on the combined stellar+nebular profile. All three issues can be tackled with recently created theoretical stellar libraries for hot stars which take into account the radiation-hydrodynamics of stellar winds.Comment: International Workshop on Stellar Spectral Libraries, Lyon (France), October 14 - 17, 2013. To be published in ASI Conference Series, 2014, Vol. 10, editors: H. P. Singh & P. Prugnie

Metals in Star-Forming Galaxies at High Redshift

The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution. Measuring abundances in distant galaxies with current techniques is often a challenge, and the canonical metallicity indicators can often not be applied. I discuss currently available metallicity indicators based on stellar and interstellar absorption and emission lines, and assess their limitations and systematic uncertainties. Recent studies suggest that star-forming galaxies at redshift around 3 have heavy-element abundances already close to solar, in agreement with predictions from cosmological models.Comment: 6 pages, 3 figures. Invited talk given at IAU Symp. 228, From Lithium to Uranium, Paris (France), 23 - 27 May, 2005. To be published in: IAU Symp. 228, From Lithium to Uranium, ed. V. Hill, P. Francois, & F. Primas (Cambridge: CUP), in pres

Revision of Star-Formation Measures

Rotation plays a major role in the evolution of massive stars. A revised grid of stellar evolutionary tracks accounting for rotation has recently been released by the Geneva group and implemented into the Starburst99 evolutionary synthesis code. Massive stars are predicted to be hotter and more luminous than previously thought, and the spectral energy distributions of young populations mirror this trend. The hydrogen ionizing continuum in particular increases by a factor of up to 3 in the presence of rotating massive stars. The effects of rotation generally increase towards shorter wavelengths and with decreasing metallicity. Revised relations between star-formation rates and monochromatic luminosities for the new stellar models are presented.Comment: 5 pages, 3 figures, to appear in IAU Symp. 255, Low-Metallicity Star Formation, ed. L. Hunt, S. Madden, & R. Schneider (Cambridge: CUP