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F stars, metallicity, and the ages of red galaxies at z > 1
Astrophysics · Submitted 27 Mar 2001
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Our results therefore continue to argue strongly against an Einstein-de Sitter universe, and favour a lambda-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3 - 5.
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We explore whether the rest-frame near-UV spectral region, observable in high-redshift galaxies via optical spectroscopy, contains sufficient information to allow the degeneracy between age and metallicity to be lifted. We do this by testing the ability of evolutionary synthesis models to reclaim the correct metallicity when fitted to the near-UV spectra of F stars of known (sub-solar and super-solar) metallicity. F stars are of particular interest because the rest-frame near-UV spectra of the oldest known elliptical galaxies at z > 1 appear to be dominated by F stars near to the main-sequence turnoff. We find that, in the case of the F stars, where the HST ultraviolet spectra have high signal:noise, model-fitting with metallicity allowed to vary as a free parameter is rather successful at deriving the correct metallicity. As a result, the estimated turnoff ages of these stars yielded by the model fitting are well constrained. Encouraged by this we have fitted these same variable- metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio galaxies 53W091 and 53W069 obtained with the Keck telescope. While the age-metallicity degeneracy is not so easily lifted for these galaxies, we find that even when metallicity is allowed as a free parameter, the best estimates of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly excluded. Furthermore, we find that a search of the entire parameter space of metallicity and star formation history using MOPED (Heavens et al., 2000) leads to the same conclusion. Our results therefore continue to argue strongly against an Einstein-de Sitter universe, and favour a lambda-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3 - 5.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We explore whether the rest-frame near-UV spectral region, observable in high-redshift galaxies via optical spectroscopy, contains sufficient information to allow the degeneracy between age and metallicity to be lifted. | contribution 0.71 | 0.31 | 0.03 | hedged possibility 0.74 |
| s1 | We do this by testing the ability of evolutionary synthesis models to reclaim the correct metallicity when fitted to the near-UV spectra of F stars of known (sub-solar and super-solar) metallicity. | method 0.98 | 0.91 | 0.02 | asserted 0.84 |
| s2 | F stars are of particular interest because the rest-frame near-UV spectra of the oldest known elliptical galaxies at z > 1 appear to be dominated by F stars near to the main-sequence turnoff. | background 0.96 | 0.11 | 0.02 | hedged possibility 0.52 |
| s3 | We find that, in the case of the F stars, where the HST ultraviolet spectra have high signal:noise, model-fitting with metallicity allowed to vary as a free parameter is rather successful at deriving the correct metallicity. | result 1.00 | 0.95 | 0.07 | asserted 1.00 |
| s4 | As a result, the estimated turnoff ages of these stars yielded by the model fitting are well constrained. | result 0.98 | 0.92 | 0.05 | asserted 1.00 |
| s5 | Encouraged by this we have fitted these same variable- metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio galaxies 53W091 and 53W069 obtained with the Keck telescope. | method 0.75 | 0.96 | 0.02 | asserted 0.97 |
| s6 | While the age-metallicity degeneracy is not so easily lifted for these galaxies, we find that even when metallicity is allowed as a free parameter, the best estimates of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly excluded. | result 1.00 | 0.97 | 0.26 | asserted 1.00 |
| s7 | Furthermore, we find that a search of the entire parameter space of metallicity and star formation history using MOPED (Heavens et al., 2000) leads to the same conclusion. | result 0.65 | 0.92 | 0.06 | asserted 1.00 |
| s8 | Our results therefore continue to argue strongly against an Einstein-de Sitter universe, and favour a lambda-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3 - 5. | interpretation 1.00 | 0.74 | 0.85 | asserted 0.64 |
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The paper
Original abstract
We explore whether the rest-frame near-UV spectral region, observable in high-redshift galaxies via optical spectroscopy, contains sufficient information to allow the degeneracy between age and metallicity to be lifted. We do this by testing the ability of evolutionary synthesis models to reclaim the correct metallicity when fitted to the near-UV spectra of F stars of known (sub-solar and super-solar) metallicity. F stars are of particular interest because the rest-frame near-UV spectra of the oldest known elliptical galaxies at z > 1 appear to be dominated by F stars near to the main-sequence turnoff. We find that, in the case of the F stars, where the HST ultraviolet spectra have high signal:noise, model-fitting with metallicity allowed to vary as a free parameter is rather successful at deriving the correct metallicity. As a result, the estimated turnoff ages of these stars yielded by the model fitting are well constrained. Encouraged by this we have fitted these same variable- metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio galaxies 53W091 and 53W069 obtained with the Keck telescope. While the age-metallicity degeneracy is not so easily lifted for these galaxies, we find that even when metallicity is allowed as a free parameter, the best estimates of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly excluded. Furthermore, we find that a search of the entire parameter space of metallicity and star formation history using MOPED (Heavens et al., 2000) leads to the same conclusion. Our results therefore continue to argue strongly against an Einstein-de Sitter universe, and favour a lambda-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3 - 5.
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2 arXiv papers cite this in 2 sentences
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Uses its data or values 1 paper
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The third subsample of sample A consists of two radio galaxies 53W091 and 53W069 [ref] .
Transition Redshift: New constraints from parametric and nonparametric methods · Age of galaxies · 1.00
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