233 research outputs found
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
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
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
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